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Physicists Suggest Link Between Dark Energy and the Arrow of Time

Physicists Suggest Link Between Dark Energy and the Arrow of Time | Amazing Science | Scoop.it

Is dark energy the reason time moves forward? For years, physicists have attempted to explain dark energy - a mysterious influence that pushes space apart faster than gravity can pull the things in it together. But physics isn’t always about figuring out what things are. A lot of it is figuring out what things cause. In a recent paper, a group of physicists asked this very question about dark energy, and found that in some cases, it might cause time to go forward.

When you throw a ball into the air, it starts with some initial speed-up, but then it slows as Earth’s gravity pulls it down. If you throw it fast enough (about 11 km per second, for those who want to try), it’ll never slow down enough to turn around and start falling back towards you, but it’ll still move more slowly as it moves away from you, because of Earth’s gravity.

Physicists and astronomers in the 1990s expected something similar to have occurred after the big bang - an event that threw matter out in all directions. The collective gravity from all that matter should have slowed it all down, just like the Earth slows down the ball. But that’s not what they found.

Instead, everything seems to have sped up. There’s something pervading the Universe that physically spreads space apart faster than gravity can pull things together. The effect is small - it’s only noticeable when you look at far-away galaxies - but it’s there. It’s become known as dark energy - "dark", because no one knows what it is.

Science is nothing if not the process of humans looking for things they can’t explain, so this isn’t the first time the Universe has stumped us. For centuries, one of those stumpers has been time itself: Why does time have an arrow pointing from the past to the present to the future?

It might seem like a silly question - I mean, if time didn’t go forward, then effects would precede causes, and that seems like it should be impossible - but it’s less of one than you might think.

The Universe, as far as we can tell, only operates according to laws of physics. And just about all of the laws of physics that we know are completely time-reversible, meaning that the things they cause look exactly the same whether time runs forward or backward.

One example is the path of a planet going around a star, which is governed by gravity. Whether time runs forward or backward, planetary orbits follow the exact same paths. The only difference is the direction of the orbit.

But one important piece of physics isn’t time-reversible, and that’s the second law of thermodynamics. It states that as time moves forward, the amount of disorder in the Universe will always increase. Just like dark energy, it’s something we’ve noticed about the Universe, and it’s something that we still don’t totally understand - though admittedly we have a better idea of it than we do of dark energy.

Physicists have, for this reason, reluctantly settled on the second law as the source of time’s arrow: disorder always has to increase after something happens, which requires that time can only move in one direction.

So physicists A. E. Allahverdyan from the Yerevan Physics Institute and V. G. Gurzadyan from Yerevan State University, both in Armenia, decided to see if - at least in a limited situation - dark energy and the second law might be related. To test it, they looked at the simple case of something like a planet orbiting a star with a changing mass.

They found that if dark energy either doesn’t exist or if it pulls space together, the planet just dully orbits the star without anything interesting happening. There’s no way to tell an orbit going forward in time from one going backward in time.

But if dark energy pushes space apart, like it does in our Universe, the planet eventually gets thrown away from the star on a path of no return. This gives us a distinction between the past and the future: run time one way, and the planet is flung off, run it the other way, and the planet comes in and gets captured by the star.

Dark energy naturally leads to an arrow of time. The authors stress that this is a really limited situation, and they’re certainly not claiming dark energy is the reason time only ever moves forward. But they’ve shown a possible link between thermodynamics and dark energy that could help us to understand either - or maybe both - better than we ever have.

The research has been published in Physical Review E.


Via Kim Frye, Tania Gammage, The Planetary Archives / San Francisco, California, CineversityTV
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Scientists Determine Mass of NGC 1332’s Supermassive Black Hole with 90% Accuracy

Scientists Determine Mass of NGC 1332’s Supermassive Black Hole with 90% Accuracy | Amazing Science | Scoop.it

NGC 1332, otherwise known as ESO 548-18 and LEDA 12838, is an almost-edge-on elliptical galaxy in the direction of the southern constellation Eridanus. The galaxy is a member of the NGC 1315–1332 group, which is approximately 80 million light-years from Earth. Like other giant elliptical galaxies, NGC 1332 hosts a supermassive black hole at its center. Working with high-resolution data from the Atacama Large Millimeter/submillimeter Array (ALMA) — a powerful array of 66 radio telescopes designed to conduct observations at millimeter and submillimeter wavelengths — in Chile, Dr. Barth and his colleagues from the United States and China were able to determine the speed of a disk of cold molecular gas and dust orbiting the galaxy NGC 1332’s central, supermassive black hole. The ALMA data show that near the disk’s center, the rotation speed of the gas reaches about 1.1 million mph (492 km per second).

 

By mapping the disk’s rotation with the high-resolution data, the team determined that the NGC 1332’s black hole has a mass of 660 million solar masses, with a measurement uncertainty of just 10%. This is among the most precise measurements for the mass of a galaxy’s central black hole. “Measuring the mass of a black hole accurately is very challenging, even with the most powerful telescopes on Earth or in space,” Dr. Barth said.

 

“ALMA has the revolutionary ability to observe disks of cold gas around supermassive black holes at small enough scales that we can clearly distinguish the black hole’s influence on the disk’s rotational speed.”

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Black Hole Merger Confirmed

Black Hole Merger Confirmed | Amazing Science | Scoop.it

Two black holes, with masses 29 and 35 times the mass of the Sun, merged to form an even bigger black hole.  The merger resulted in three entire suns worth of matter converted to pure energy in the form of gravitational waves. The waves travelled a billion light years before a tiny meat-filled species on a pale blue dot in space figured how to see them.  Thanks to the smartest one that species had seen in a century, they knew that black holes might merge, and that they would produce these waves if they ever collided.  They put so much trust in his proven theory, that they searched for many years to find the waves he predicted.  Exactly 100 years after his famous theory was released, their hard work paid off, and they celebrated one of the most significant discoveries in meat-filled history.


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Winds a quarter the speed of light spotted leaving mysterious binary systems

Winds a quarter the speed of light spotted leaving mysterious binary systems | Amazing Science | Scoop.it

Two black holes in nearby galaxies have been observed devouring their companion stars at a rate exceeding classically understood limits, and in the process, kicking out matter into surrounding space at astonishing speeds of around a quarter the speed of light.

 

The researchers, from the University of Cambridge, used data from the European Space Agency's (ESA) XMM-Newton space observatory to reveal for the first time strong winds gusting at very high speeds from two mysterious sources of x-ray radiation. The discovery, published in the journal Nature, confirms that these sources conceal a compact object pulling in matter at extraordinarily high rates.

 

When observing the Universe at x-ray wavelengths, the celestial sky is dominated by two types of astronomical objects: supermassive black holes, sitting at the centres of large galaxies and ferociously devouring the material around them, and binary systems, consisting of a stellar remnant - a white dwarf, neutron star or black hole - feeding on gas from a companion star.

 

In both cases, the gas forms a swirling disc around the compact and very dense central object. Friction in the disc causes the gas to heat up and emit light at different wavelengths, with a peak in x-rays. But an intermediate class of objects was discovered in the 1980s and is still not well understood. Ten to a hundred times brighter than ordinary x-ray binaries, these sources are nevertheless too faint to be linked to supermassive black holes, and in any case, are usually found far from the centre of their host galaxy.

 

"We think these so-called 'ultra-luminous x-ray sources' are special binary systems, sucking up gas at a much higher rate than an ordinary x-ray binary," said Dr Ciro Pinto from Cambridge's Institute of Astronomy, the paper's lead author. "Some of these sources host highly magnetised neutron stars, while others might conceal the long-sought-after intermediate-mass black holes, which have masses around one thousand times the mass of the Sun. But in the majority of cases, the reason for their extreme behaviour is still unclear."

 

Pinto and his colleagues collected several days' worth of observations of three ultra-luminous x-ray sources, all located in nearby galaxies located less than 22 million light-years from the Milky Way. The data was obtained over several years with the Reflection Grating Spectrometer on XMM-Newton, which allowed the researchers to identify subtle features in the spectrum of the x-rays from the sources. In all three sources, the scientists were able to identify x-ray emission from gas in the outer portions of the disc surrounding the central compact object, slowly flowing towards it.

 

But two of the three sources - known as NGC 1313 X-1 and NGC 5408 X-1 - also show clear signs of x-rays being absorbed by gas that is streaming away from the central source at 70,000 kilometres per second - almost a quarter of the speed of light. "This is the first time we've seen winds streaming away from ultra-luminous x-ray sources," said Pinto. "And the very high speed of these outflows is telling us something about the nature of the compact objects in these sources, which are frantically devouring matter."

 

While the hot gas is pulled inwards by the central object's gravity, it also shines brightly, and the pressure exerted by the radiation pushes it outwards. This is a balancing act: the greater the mass, the faster it draws the surrounding gas; but this also causes the gas to heat up faster, emitting more light and increasing the pressure that blows the gas away. There is a theoretical limit to how much matter can be pulled in by an object of a given mass, known as the Eddington limit. The limit was first calculated for stars by astronomer Arthur Eddington, but it can also be applied to compact objects like black holes and neutron stars.

 

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The black-hole collision that reshaped physics

The black-hole collision that reshaped physics | Amazing Science | Scoop.it
A momentous signal from space has confirmed decades of theorizing on black holes — and launched a new era of gravitational-wave astronomy.

 

The event was catastrophic on a cosmic scale — a merger of black holes that violently shook the surrounding fabric of space and time, and sent a blast of space-time vibrations known as gravitational waves rippling across the Universe at the speed of light. But it was the kind of calamity that physicists on Earth had been waiting for. On 14 September, when those ripples swept across the freshly upgraded Laser Interferometer Gravitational-Wave Observatory (Advanced LIGO), they showed up as spikes in the readings from its two L-shaped detectors in Louisiana and Washington state. For the first time ever, scientists had recorded a gravitational-wave signal.

 

“There it was!” says LIGO team member Daniel Holz, an astrophysicist at the University of Chicago in Illinois. “And it was so strong, and so beautiful, in both detectors.” Although the shape of the signal looked familiar from the theory, Holz says, “it's completely different when you see something in the data. It's this transcendent moment”.

 

The signal, formally designated GW150914 after the date of its occurrence and informally known to its discoverers as 'the Event', has justly been hailed as a milestone in physics. It has provided a wealth of evidence for Albert Einstein's century-old general theory of relativity, which holds that mass and energy can warp space-time, and that gravity is the result of such warping. Stuart Shapiro, a specialist in computer simulations of relativity at the University of Illinois at Urbana–Champaign, calls it “the most significant confirmation of the general theory of relativity since its inception”.

 

But the Event also marks the start of a long-promised era of gravitational-wave astronomy. Detailed analysis of the signal has already yielded insights into the nature of the black holes that merged, and how they formed. With more events such as these — the LIGO team is analysing several other candidate events captured during the detectors' four-month run, which ended in January — researchers will be able to classify and understand the origins of black holes, just as they are doing with stars.

 

Still more events should appear starting in September, when Advanced LIGO is scheduled to begin joint observations with its European counterpart, the Franco–Italian-led Advanced Virgo facility near Pisa, Italy. (The two collaborations already pool data and publish papers together.) This detector will not only contribute crucial details to events, but could also help astronomers to make cosmological-distance measurements more accurately than before.

 

“It's going to be a really good ride for the next few years,” says Bruce Allen, managing director of the Max Planck Institute for Gravitational Physics in Hanover, Germany. “The more black holes they see whacking into each other, the more fun it will be,” says Roger Penrose, a theoretical physicist and mathematician at the University of Oxford, UK, whose work in the 1960s helped to lay the foundation for the theory of the objects. “Suddenly, we have a new way of looking at the Universe.”

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Measurement of Universe's expansion rate creates cosmological puzzle

Measurement of Universe's expansion rate creates cosmological puzzle | Amazing Science | Scoop.it

The most precise measurement ever made of the current rate of expansion of the Universe has produced a value that appears incompatible with measurements of radiation left over from the Big Bang1. If the findings are confirmed by independent techniques, the laws of cosmology might have to be rewritten.

 

 

This might even mean that dark energy — the unknown force that is thought to be responsible for the observed acceleration of the expansion of the Universe — has increased in strength since the dawn of time. “I think that there is something in the standard cosmological model that we don't understand,” says astrophysicist Adam Riess, a physicist at Johns Hopkins University in Baltimore, Maryland, who co-discovered dark energy in 1998 and led the latest study.

 

Kevork Abazajian, a cosmologist at the University of California, Irvine, who was not involved in the study, says that the results have the potential of “becoming transformational in cosmology”.

 

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Possible signature of dark matter annihilation detected

Possible signature of dark matter annihilation detected | Amazing Science | Scoop.it

We live in a dramatic epoch of astrophysics. Breakthrough discoveries like exoplanets, gravitational waves from merging black holes, or cosmic acceleration seem to arrive every decade, or even more often. But perhaps no discovery was more unexpected, mysterious, and challenging to our grasp of the "known universe" than the recognition that the vast majority of matter in the universe cannot be directly seen. This matter is dubbed "dark matter," and its nature is unknown. According to the latest results from the Planck satellite, a mere 4.9% of the universe is made of ordinary matter (that is, matter composed of atoms or their constituents). The rest is dark matter, and it has been firmly detected via its gravitational influence on stars and other normal matter. Dark energy is a separate constituent.

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Astronomers see unprecedented detail of inner portion of protoplanetary disk

Astronomers see unprecedented detail of inner portion of protoplanetary disk | Amazing Science | Scoop.it
Astronomers have discovered details of the inner, thickest portion of a dusty disk surrounding a young star and provided new insight on the earliest stages of planet formation.

 

New images of a young star made with the Karl G. Jansky Very Large Array (VLA) reveal what scientists think may be the very earliest stages in the formation of planets. The scientists used the VLA to see unprecedented detail of the inner portion of a dusty disk surrounding the star, some 450 light-years from Earth.

 

The star and its disk were studied in 2014 with the Atacama Large Millimeter/submillimeter Array (ALMA), which produced what astronomers then called the best image ever of planet formation in progress. The ALMA image showed gaps in the disk, presumably caused by planet-like bodies sweeping out the dust along their orbits. This image, showing in real life what theorists had proposed for years, was surprising, however, because the star, called HL Tau, is only about a million years old -- very young by stellar standards.

 

The ALMA image showed details of the system in the outer portions of the disk, but in the inner portions of the disk, nearest to the young star, the thicker dust is opaque to the short radio wavelengths received by ALMA. To study this region, astronomers turned to the VLA, which receives longer wavelengths. Their VLA images show that region better than any previous studies.

 

The new VLA images revealed a distinct clump of dust in the inner region of the disk. The clump, the scientists said, contains roughly 3 to 8 times the mass of the Earth.

"We believe this clump of dust represents the earliest stage in the formation of protoplanets, and this is the first time we've seen that stage," said Thomas Henning, of the Max Planck Institute for Astronomy (MPIA).

 

"This is an important discovery, because we have not yet been able to observe most stages in the process of planet formation," said Carlos Carrasco-Gonzalez from the Institute of Radio Astronomy and Astrophysics (IRyA) of the National Autonomous University of Mexico (UNAM). "This is quite different from the case of star formation, where, in different objects, we have seen stars in different stages of their life cycle. With planets, we haven't been so fortunate, so getting a look at this very early stage in planet formation is extremely valuable," he added.

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Black Holes and Black Hole Tech. How far have we progressed?

Black Holes and Black Hole Tech. How far have we progressed? | Amazing Science | Scoop.it
In celebration of the detection of gravitational waves, Stephen Wolfram looks forward and discusses what technology black holes could make possible.
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Winds from Hell: Fastest winds ever have been discovered near a supermassive black hole

Winds from Hell: Fastest winds ever have been discovered near a supermassive black hole | Amazing Science | Scoop.it

The fastest winds ever seen at ultraviolet wavelengths have been discovered near a supermassive black hole. “This new ultrafast wind surprised us when it appeared at ultraviolet wavelengths, indicating it is racing away from the ravenous black hole at unprecedented speeds—almost like a bat out of hell,” says William Nielsen (Niel) Brandt, professor of astronomy and astrophysics and a professor of physics at Penn State. “We’re talking wind speeds of more than 200 million miles an hour, equivalent to a category 77 hurricane,” says Jesse Rogerson, who led the research as part of his efforts toward earning a PhD in the physics and astronomy department at York University in Canada.

 

The ultraviolet-wavelength winds are coming from the black hole’s quasar—the disk of hot gas that surrounds the black hole. Quasars form around supermassive black holes at the centers of massive galaxies. Quasars are bigger than Earth’s orbit around the Sun and hotter than the surface of the Sun, generating enough light to be seen across the observable universe. “An exciting discovery in recent years has been the realization that ultraviolet winds from quasars can both appear and disappear when viewed from Earth, depending on various conditions surrounding the black hole,” Brandt says.

 

“Black holes can have a mass that is billions of times larger than the Sun, mostly because they are messy eaters in a way, capturing any material that ventures too close,” says Patrick Hall, associate professor at York University. “But as matter spirals toward a black hole, some of it is blown away by the heat and light of the quasar. These are the winds that we are detecting.”

 

The researchers used data from the Sloan Digital Sky Survey (SDSS) to identify new outflows from quasars. After spotting about 300 examples, they selected about 100 for further exploration, collecting data with the Gemini Observatory’s twin telescopes in Hawaii and Chile. Much of the research is aimed at better understanding outflows from quasars and why they happen. “Quasar winds play an important role in galaxy formation,” Rogerson says.

 

“When galaxies form, these winds fling material outwards and deter the creation of stars. If such winds didn’t exist or were less powerful, we would see far more stars in big galaxies than we actually do. Hubble Space Telescope images of galaxies would look much different if quasar winds did not exist.”

 

The study is published in the Monthly Notices of the Royal Astronomical Society.

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Revealing the Nature of Dark Matter

Dr. Dan Hooper, a Theoretical Astrophysicist at Fermilab, explores the current status of the dark matter search and some new thoughts on the nature of this mystery.

A signal of gamma rays has been observed from the center of the Milky Way, and it may be the breakthrough that we have long been waiting for. If these gamma-rays are in fact being produced by the interactions of dark matter particles, they promise to reveal much about this elusive substance, and may be a major step toward identifying of the underlying nature of our universe's dark matter.
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Mysterious cosmic radio bursts found to repeat

Mysterious cosmic radio bursts found to repeat | Amazing Science | Scoop.it

Astronomers for the first time have detected repeating short bursts of radio waves from an enigmatic source that is likely located well beyond the edge of our Milky Way galaxy. The findings indicate that these "fast radio bursts" come from an extremely powerful object which occasionally produces multiple bursts in under a minute.

 

Prior to this discovery, reported in Nature, all previously detected fast radio bursts (FRBs) have appeared to be one-off events. Because of that, most theories about the origin of these mysterious pulses have involved cataclysmic incidents that destroy their source - a star exploding in a supernova, for example, or a neutron star collapsing into a black hole. The new finding, however, shows that at least some FRBs have other origins.

FRBs, which last just a few thousandths of a second, have puzzled scientists since they were first reported nearly a decade ago. Despite extensive follow-up efforts, astronomers until now have searched in vain for repeat bursts.

 

That changed last November 5th, when McGill University PhD student Paul Scholz was sifting through results from observations performed with the Arecibo radio telescope in Puerto Rico - the world's largest radio telescope. The new data, gathered in May and June and run through a supercomputer at the McGill High Performance Computing Centre, showed several bursts with properties consistent with those of an FRB detected in 2012.

 

The repeat signals were surprising - and "very exciting," Scholz says. "I knew immediately that the discovery would be extremely important in the study of FRBs." As his office mates gathered around his computer screen, Scholz pored over the remaining output from specialized software used to search for pulsars and radio bursts. He found that there were a total of 10 new bursts.

 

The finding suggests that these bursts must have come from a very exotic object, such as a rotating neutron star having unprecedented power that enables the emission of extremely bright pulses, the researchers say. It is also possible that the finding represents the first discovery of a sub-class of the cosmic fast-radio-burst population.


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Pulsar Web Could Detect Low-Frequency Gravitational Waves

Pulsar Web Could Detect Low-Frequency Gravitational Waves | Amazing Science | Scoop.it
Monitoring a vast network of rapidly spinning pulsars is key to finding very-low-frequency gravitational waves, researchers say.


Pulsars emit beams of radio waves, some of which sweep across Earth once every rotation. Astronomers detect this as a rapid pulse of radio emission. Most pulsars rotate several times a second. But some, called millisecond pulsars, rotate hundreds of times faster.


"Millisecond pulsars have extremely predictable arrival times, and our instruments are able to measure them to within a ten-millionth of a second," said Maura McLaughlin, a radio astronomer at West Virginia University in Morgantown and member of the NANOGrav team. "Because of that, we can use them to detect incredibly small shifts in Earth's position."


But astrophysicists at JPL and Caltech caution that detecting faint gravitational waves would likely require more than a few pulsars. "We're like a spider at the center of a web," said Michele Vallisneri, another member of the JPL/Caltech research group. "The more strands we have in our web of pulsars, the more likely we are to sense when a gravitational wave passes by."


Vallisneri said accomplishing this feat will require international collaboration. "NANOGrav is currently monitoring 54 pulsars, but we can only see some of the southern hemisphere. We will need to work closely with our colleagues in Europe and Australia in order to get the all-sky coverage this search requires."


The feasibility of this approach was recently called into question when a group of Australian pulsar researchers reported that they were unable to detect such signals when analyzing a set of pulsars with the most precise timing measurements. After studying this result, the NANOGrav team determined that the reported non-detection was not a surprise, and resulted from the combination of optimistic gravitational wave models and analysis of too few pulsars. Theirone-page response was released recently via the arXiv electronic print service.


Despite the technical challenges, Taylor is confident their team is on the right track. "Gravitational waves are washing over Earth all the time," Taylor said. "Given the number of pulsars being observed by NANOGrav and other international teams, we expect to have clear and convincing evidence of low-frequency gravitational waves within the next decade."


NANOGrav is a collaboration of over 60 scientists at more than a dozen institutions in the United States and Canada. The group uses radio pulsar timing observations acquired at NRAO's Green Bank Telescope in West Virginia and at Arecibo Radio Observatory in Puerto Rico to search for ripples in the fabric of spacetime. In 2015, NANOGrav was awarded $14.5 million by the National Science Foundation to create and operate a Physics Frontiers Center.


"With the recent detection of gravitational waves by LIGO, the outstanding work of the NANOGrav collaboration is particularly relevant and timely," said Pedro Marronetti, National Science Foundation program director for gravitational wave research. "This NSF-funded Physics Frontier Center is poised to complement LIGO observations, extending the window of gravitational wave detection to very low frequencies."

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Astronomers confirm faintest early-universe galaxy ever seen

Astronomers confirm faintest early-universe galaxy ever seen | Amazing Science | Scoop.it

An international team of scientists, including two professors and three graduate students from UCLA, has detected and confirmed the faintest early-universe galaxy ever. Using the W. M. Keck Observatory on the summit on Mauna Kea in Hawaii, the researchers detected the galaxy as it was 13 billion years ago. The results were published in the Astrophysical Journal Letters.

 

Tommaso Treu, a professor of physics and astronomy in the UCLA College and a co-author of the research, said the discovery could be a step toward unraveling one of the biggest mysteries in astronomy: how a period known as the "cosmic dark ages" ended.

 

The researchers made the discovery using an effect called gravitational lensing to see the incredibly faint object, which was born just after the Big Bang. Gravitational lensing was first predicted by Albert Einstein almost a century ago; the effect is similar to that of an image behind a glass lens appearing distorted because of how the lens bends light. The detected galaxy was behind a galaxy cluster known as MACS2129.4-0741, which is massive enough to create three different images of the galaxy.

 

According to the Big Bang theory, the universe cooled as it expanded. As that happened, Treu said, protons captured electrons to form hydrogen atoms, which in turn made the universe opaque to radiation -- giving rise to the cosmic dark ages.

 

"At some point, a few hundred million years later, the first stars formed and they started to produce ultraviolet light capable of ionizing hydrogen," Treu said. "Eventually, when there were enough stars, they might have been able to ionize all of the intergalactic hydrogen and create the universe as we see it now."

 

That process, called cosmic reionization, happened about 13 billion years ago, but scientists have so far been unable to determine whether there were enough stars to do it or whether more exotic sources, like gas falling onto supermassive black holes, might have been responsible.

 

"Currently, the most likely suspect is stars within faint galaxies that are too faint to see with our telescopes without gravitational lensing magnification," Treu said. "This study exploits gravitational lensing to demonstrate that such galaxies exist, and is thus an important step toward solving this mystery."

 

The research team was led by Marusa Bradac, a professor at UC Davis. Co-authors include Matthew Malkan, a UCLA professor of physics and astronomy, and UCLA graduate students Charlotte Mason, Takahiro Morishita and Xin Wang.

The galaxy's magnified spectra were detected independently by both Keck Observatory and Hubble Space Telescope data.

 

 

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Dark Matter Keeps us Still in the Dark

Dark Matter Keeps us Still in the Dark | Amazing Science | Scoop.it

Dark matter has an interesting history.  It was first proposed to account for the fact that stars in our galaxy move much faster than they should around the galactic core. Evidence of dark matter has been seen in galactic collisions like the Bullet Cluster, as well as through gravitational lensing by galaxies. On the other hand, we have yet to find any direct detection of dark matter particles. In fact, many of the likely candidates for dark matter have been all but eliminated. Then there is thepuzzling aspect of dwarf galaxies.

 

Although dark matter (specifically cold dark matter) works well on large cosmic scales and within large galaxies such as the Milky Way, it doesn’t seem to match up well with dwarf galaxies for several reasons.  One of this is that computer simulations of dark matter predict that spiral galaxies should have many more satellite dwarf galaxies than they actually do.  For example, models predict that the Milky Way should have about 500 satellite galaxies, which in reality it has only 11.  It should also be the case that these satellite galaxies orbit the main galaxy in random directions, but studies of the Andromeda galaxy finds that satellites are somewhat clustered in a plane.  So either something is up with dark matter, or there is an issue with the simulations.

 

Another problem with dwarf galaxies is known as the cuspy halo (or core-cusp) problem.  Basically if dark matter is “cold”, it should gravitationally clump toward the center of a mass.  This means the distribution of a galaxy’s dark matter halo should have a cusp in the center.  We don’t see such dark matter clumping, even in our own galaxy. This is a particular problem in diffuse dwarf galaxies known as low surface brightness galaxies, or LSBs. With spiral galaxies such a the Milky way, you can argue that the central core of regular matter masks the effects of a dark matter cusp. But since LSBs are diffuse, and they still no cusp of dark matter, that argument isn’t very compelling.

 

So what if dark matter is wrong?  The main alternative to dark matter are a range of modified gravity models.  These propose that on galactic scales gravity differs from the form described by general relativity.  The most popular of these modified gravity models is known as modified Newtonian dynamics, or MoND.  It turns out that MoND works really well for LSB galaxies.  The stellar motion of LSBs matches the predictions of MoND, so you could call it a win for modified gravity. But modified gravity also has several major problems.  It doesn’t account for effects such as the Bullet Cluster, it is completely contradicted by the clustering of galaxies on large cosmic scales, and it incorrectly predicts the motions of galaxies within clusters.

 

So where does that leave us? At this point it is generally thought that dark matter not only exists, it accounts for most if not all of the effects we see. We have enough observational evidence to support the existence of dark matter, and effects such as large scale clustering can’t be described by any modified gravity model that also agrees with the experimental limits of special and general relativity.  The big question is whether dark matter can account for all the effects such as LSBs, which it hasn’t done so far. Without a direct observation of dark matter, all sorts of variations have been proposed that might solve the LSB problem among others.

 

The alternative is that in addition to dark matter there is some new gravitational effect.  Right now most astrophysicists don’t see that as very likely, but if we detect a type of dark matter that can’t account for dwarf galaxies, then it will be clear that modified gravity also plays a role. If that happens, it could revolutionize our understanding of the universe. It would require an extension of Newton and Einstein that are currently the foundation of modern cosmology.

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Fermi Links Neutrino Blast To Known Extragalactic Blazar - Universe Today

Fermi Links Neutrino Blast To Known Extragalactic Blazar - Universe Today | Amazing Science | Scoop.it

A unique observatory buried deep in the clear ice of the South Pole region, an orbiting observatory that monitors gamma rays, a powerful outburst from a black hole 10 billion light years away, and a super-energetic neutrino named Big Bird. These are the cast of characters that populate a paper published in Nature Physics, on Monday April 18th.

 

The observatory that resides deep in the cold dark of the Antarctic ice has one job: to detect neutrinos. Neutrinos are strange, standoffish particles, sometimes called ‘ghost particles’ because they’re so difficult to detect. They’re like the noble gases of the particle world. Though neutrinos vastly outnumber all other atoms in our Universe, they rarely interact with other particles, and they have no electrical charge. This allows them to pass through normal matter almost unimpeded. To even detect them, you need a dark, undisturbed place, isolated from cosmic rays and background radiation.

 

This explains why they built an observatory in solid ice. This observatory, called the IceCube Neutrino Observatory, is the ideal place to detect neutrinos. On the rare occasion when a neutrino does interact with the ice surrounding the observatory, a charged particle is created. This particle can be either an electron, muon, or tau. If these charged particles are of sufficiently high energy, then the strings of detectors that make up IceCube can detect it. Once this data is analyzed, the source of the neutrinos can be known.

 

The next actor in this scenario is NASA’s Fermi Gamma-Ray Space Telescope. Fermi was launched in 2008, with a specific job in mind. Its job is to look at some of the exceptional phenomena in our Universe that generate extraordinarily large amounts of energy, like super-massive black holes, exploding stars, jets of hot gas moving at relativistic speeds, and merging neutron stars. These things generate enormous amounts of gamma-ray energy, the part of the electromagnetic spectrum that Fermi looks at exclusively.

 

Next comes PKS B1424-418, a distant galaxy with a black hole at its center. About 10 billion years ago, this black hole produced a powerful outburst of energy, called a blazar because it’s pointed at Earth. The light from this outburst started arriving at Earth in 2012. For a year, the blazar in PKS B1424-418 shone 15-30 times brighter in the gamma spectrum than it did before the burst.

 

Detecting neutrinos is a rare occurrence. So far, IceCube has detected about a hundred of them. For some reason, the most energetic of these neutrinos are named after characters on the popular children’s show called Sesame Street. In December 2012, IceCube detected an exceptionally energetic neutrino, and named it Big Bird. Big Bird had an energy level greater than 2 quadrillion electron volts. That’s an enormous amount of energy shoved into a particle that is thought to have less than one millionth the mass of an electron.

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The Universe, where space-time becomes discrete

The Universe, where space-time becomes discrete | Amazing Science | Scoop.it
A theoretical study has analyzed a model that saves special relativity and reconciles it with granularity by introducing small-scale deviations from the principle of locality demonstrating that it can be experimentally tested with great precision.

 

Our experience of space-time is that of a continuous object, without gaps or discontinuities, just as it is described by classical physics. For some quantum gravity models however, the texture of space-time is "granular" at tiny scales (below the so-called Planck scale, 10-33 cm), as if it were a variable mesh of solids and voids (or a complex foam). One of the great problems of physics today is to understand the passage from a continuous to a discrete description of spacetime: is there an abrupt change or is there gradual transition? Where does the change occur?

 

The separation between one world and the other creates problems for physicists: for example, how can we describe gravity -- explained so well by classical physics -- according to quantum mechanics? Quantum gravity is in fact a field of study in which no consolidated and shared theories exist as yet. There are, however, "scenarios," which offer possible interpretations of quantum gravity subject to different constraints, and which await experimental confirmation or confutation.

 

One of the problems to be solved in this respect is that if space-time is granular beyond a certain scale it means that there is a "basic scale," a fundamental unit that cannot be broken down into anything smaller, a hypothesis that clashes with Einstein's theory of special relativity. Imagine holding a ruler in one hand: according to special relativity, to an observer moving in a straight line at a constant speed (close to the speed of light) relative to you, the ruler would appear shorter. But what happens if the ruler has the length of the fundamental scale? For special relativity, the ruler would still appear shorter than this unit of measurement. Special relativity is therefore clearly incompatible with the introduction of a basic graininess of spacetime. Suggesting the existence of this basic scale, say the physicists, means to violate Lorentz invariance, the fundamental tenet of special relativity.

 

So how can the two be reconciled? Physicists can either hypothesize violations of Lorentz invariance, but have to satisfy very strict constraints (and this has been the preferred approach so far), or they must find a way to avoid the violation and find a scenario that is compatible with both granularity and special relativity. This scenario is in fact implemented by some quantum gravity models such as String Field Theory and Causal Set Theory. The problem to be addressed, however, was how to test their predictions experimentally given that the effects of these theories are much less apparent than are those of the models that violate special relativity. One solution to this impasse has now been put forward by Stefano Liberati, SISSA professor, and colleagues in their latest publication. The study was conducted with the participation of researchers from the LENS in Florence (Francesco Marin and Francesco Marino) and from the INFN in Padua (Antonello Ortolan). Other SISSA scientists taking part in the study, in addition to Liberati, were PhD student Alessio Belenchia and postdoc Dionigi Benincasa. The research was funded by a grant of the John Templeton Foundation.

"We respect Lorentz invariance, but everything comes at a price, which in this case is the introduction of non-local effects," comments Liberati. The scenario studied by Liberati and colleagues in fact salvages special relativity but introduces the possibility that physics at a certain point in space-time can be affected by what happens not only in proximity to that point but also at regions very far from it. "Clearly we do not violate causality nor do we presuppose information that travels faster than light," points out the scientist. "We do, however, introduce a need to know the global structure so as to understand what's going on at a local level."

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Einstein Ring: Dwarf Dark Galaxy Hidden in ALMA Gravitational Lens Image

Einstein Ring: Dwarf Dark Galaxy Hidden in ALMA Gravitational Lens Image | Amazing Science | Scoop.it

Subtle distortions hidden in ALMA’s stunning image of the gravitational lens SDP.81 are telltale signs that a dwarf dark galaxy is lurking in the halo of a much larger galaxy nearly 4 billion light-years away. This discovery paves the way for ALMA to find many more such objects and could help astronomers address important questions on the nature of dark matter.

In 2014, as part of ALMA’s Long Baseline Campaign, astronomers studied a variety of astronomical objects to test the telescope's new, high-resolution capabilities. One of these experimental images was that of an Einstein ring, which was produced by the gravity of a massive foreground galaxy bending the light emitted by another galaxy nearly 12 billion light-years away.

This phenomenon, called gravitational lensing, was predicted by Einstein’s general theory of relativity and it offers a powerful tool for studying galaxies that are otherwise too distant to observe. It also sheds light on the properties of the nearby lensing galaxy because of the way its gravity distorts and focuses light from more distant objects.

In a new paper accepted for publication in the Astrophysical Journal, astronomer Yashar Hezaveh at Stanford University in California and his team explain how detailed analysis of this widely publicized image uncovered signs of a hidden dwarf dark galaxy in the halo of the more nearby galaxy.

"We can find these invisible objects in the same way that you can see rain droplets on a window. You know they are there because they distort the image of the background objects,” explained Hezaveh. In the case of a rain drop, the image distortions are caused by refraction. In this image, similar distortions are generated by the gravitational influence of dark matter.

Current theories suggest that dark matter, which makes up about 80 percent of the mass of the Universe, is made of as-yet-unidentified particles that don’t interact with visible light or other forms of electromagnetic radiation. Dark matter does, however, have appreciable mass, so it can be identified by its gravitational influence.

For their analysis, the researchers harnessed thousands of computers working in parallel for many weeks, including the National Science Foundation's most powerful supercomputer, Blue Waters, to search for subtle anomalies that had a consistent and measurable counterpart in each "band" of radio data. From these combined computations, the researchers were able to piece together an unprecedented understanding of the lensing galaxy’s halo, the diffuse and predominantly star-free region around the galaxy, and discovered a distinctive clump less than one-thousandth the mass of the Milky Way.

Because of its relationship to the larger galaxy, estimated mass, and lack of an optical counterpart, the astronomers believe this gravitational anomaly may be caused by an extremely faint, dark-matter dominated satellite of the lensing galaxy. According to theoretical predictions, most galaxies should be brimming with similar dwarf galaxies and other companion objects. Detecting them, however, has proven challenging. Even around our own Milky Way, astronomers can identify only 40 or so of the thousands of satellite objects that are predicted to be present.

"This discrepancy between observed satellites and predicted abundances has been a major problem in cosmology for nearly two decades, even called a 'crisis' by some researchers," said Neal Dalal of the University of Illinois, a member of the team. "If these dwarf objects are dominated by dark matter, this could explain the discrepancy while offering new insights into the true nature of dark matter," he added.

Computer models of the evolution of the Universe indicate that by measuring the “clumpiness” of dark matter, it’s possible to measure its temperature. So by counting the number of small dark matter clumps around distant galaxies, astronomers can infer the temperature of dark matter, which has an important bearing on the smoothness of our Universe.

"If these halo objects are simply not there," notes co-author Daniel Marrone of the University of Arizona, "then our current dark matter model cannot be correct and we will have to modify what we think we understand about dark matter particles." 

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Humongous black hole catches astronomers totally off guard

Humongous black hole catches astronomers totally off guard | Amazing Science | Scoop.it
Astronomers weren't expecting to find a supermassive black hole in this average-size galaxy, and they now may have to rethink their models.

 

One of the biggest black holes ever found sits in a cosmic backwater, like a towering skyscraper in a small town.

Astronomers have spotted a supermassive black hole containing 17 billion times the mass of the sun — only slightly smaller than the heftiest known black hole, which weighs in at a maximum of 21 billion solar masses — at the center of the galaxy NGC 1600.

 

That's a surprise, because NGC 1600, which lies 200 million light-years from Earth in the constellation Eridanus, belongs to an average-size galaxy group, and the monster black holes discovered to date tend to be found in dense clusters of galaxies. So researchers may have to rethink their ideas about where gigantic black holes reside, and how many of them might populate the universe, study team members said.

 

"This black hole is much bigger than we expected for the size of the galaxy or where this galaxy lives, the environment," said study co-author Chung-Pei Ma, an astronomer at the University of California, Berkeley.

 

"That's the puzzling part — or the intriguing part — of the result," she told Space.com. "There may be more NGC 1600s out there lurking at more ordinary sites, like small towns in the U.S. rather than Manhattan."Ma is head of the MASSIVE Survey, a multitelescope effort that began in 2014 to identify and catalogue the most massive nearby galaxies and black holes. NGC 1600 first showed up in the survey with data from the McDonald Observatory in Texas.

 

Although the initial observations weren't detailed enough to see the spectrum of light from the galaxy's center clearly, Ma and her colleagues could already tell that they were looking at something extraordinary: "It was a little bit like looking at a hurricane from very far away," she said. "We couldn't quite tell how big this hurricane was, this black hole was, but the hurricane was so big that we already started to feel the wind using this coarser data."

 

Suspecting they had spotted a very large black hole, study team members next investigated the elliptical galaxy using the northern half of the Gemini Observatory, twin telescopes situated in Hawaii and Chile. Gemini allowed them to probe the black hole's "sphere of influence," Ma said — the region where the black hole's mass held more sway than the overall galaxy's, where it was whipping the stars into action. They also scoped out the site with data from NASA's Hubble Space Telescope. The stars "were going so fast that the only way they could be travelling at this speed is if you had a 17-billion-solar-mass black hole at the center," she said.

 

The largest supermassive black hole ever found contains up to 21 billion times the mass of the sun, and resides in a more expected location: the incredibly dense Coma Cluster, which includes more than 1,000 identified galaxies. For comparison, the black hole lurking at the center of the Milky Way totals around 4 million solar masses.

 

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The black-hole collision that reshaped physics

The black-hole collision that reshaped physics | Amazing Science | Scoop.it

The event was catastrophic on a cosmic scale — a merger of black holes that violently shook the surrounding fabric of space and time, and sent a blast of space-time vibrations known as gravitational waves rippling across the Universe at the speed of light.

 

But it was the kind of calamity that physicists on Earth had been waiting for. On 14 September, when those ripples swept across the freshly upgraded Laser Interferometer Gravitational-Wave Observatory (Advanced LIGO), they showed up as spikes in the readings from its two L-shaped detectors in Louisiana and Washington state. For the first time ever, scientists had recorded a gravitational-wave signal.

 

“There it was!” says LIGO team member Daniel Holz, an astrophysicist at the University of Chicago in Illinois. “And it was so strong, and so beautiful, in both detectors.” Although the shape of the signal looked familiar from the theory, Holz says, “it's completely different when you see something in the data. It's this transcendent moment”.

 

The signal, formally designated GW150914 after the date of its occurrence and informally known to its discoverers as 'the Event', has justly been hailed as a milestone in physics. It has provided a wealth of evidence for Albert Einstein's century-old general theory of relativity, which holds that mass and energy can warp space-time, and that gravity is the result of such warping. Stuart Shapiro, a specialist in computer simulations of relativity at the University of Illinois at Urbana–Champaign, calls it “the most significant confirmation of the general theory of relativity since its inception”.

 

But the Event also marks the start of a long-promised era of gravitational-wave astronomy. Detailed analysis of the signal has already yielded insights into the nature of the black holes that merged, and how they formed. With more events such as these — the LIGO team is analysing several other candidate events captured during the detectors' four-month run, which ended in January — researchers will be able to classify and understand the origins of black holes, just as they are doing with stars.

 

Still more events should appear starting in September, when Advanced LIGO is scheduled to begin joint observations with its European counterpart, the Franco–Italian-led Advanced Virgo facility near Pisa, Italy. (The two collaborations already pool data and publish papers together.) This detector will not only contribute crucial details to events, but could also help astronomers to make cosmological-distance measurements more accurately than before.

 

“It's going to be a really good ride for the next few years,” says Bruce Allen, managing director of the Max Planck Institute for Gravitational Physics in Hanover, Germany.

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Astronomers see supernova shockwave for first time

Astronomers see supernova shockwave for first time | Amazing Science | Scoop.it

The shockwave generated by the explosion of an ageing giant star has been observed for the first time by an international team of astronomers.

 

The discovery, accepted for publishing in the Astrophysical Journal, will help scientists understand the life cycle of stars, said study co-author Brad Tucker of the Australian National University.

 

"This is the first time we've seen this in the normal visible colours, and we now know it happens," Dr Tucker said.

"The fundamental way we believe that core collapse happens is related to this shockwave happening. So the physics has been around … for decades and we've finally now been able to physically examine and test what's going on."

 

The team of scientists observed the earliest moments of two old stars exploding using the Kepler Space Telescope. They spotted the shockwave around the smaller of the two stars — a red supergiant over 270 times the radius of the Sun and 750 million light years away. As the star ran out of fuel it began collapsing and compressing on its central core.

 

"It's like packing in dirt," Dr Tucker said. "You keep pressing it till it's so dense you can't get it in anymore, and that's when you create a neutron star. "But you reach a limit when you can't pack it in anymore, and that force pushing in bounces back and it triggers a shockwave to go through the star, causing the star to actually blow up."

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Beyond today's crowdsourced science to tomorrow's citizen science cyborgs

Beyond today's crowdsourced science to tomorrow's citizen science cyborgs | Amazing Science | Scoop.it
Computers are getting better and better at the jobs that previously made sense for researchers to outsource to citizen scientists. But don't worry: there's still a role for people in these projects.

 

We’re now entering an era in which machines are starting to become competitive with humans in terms of analyzing images, a task previously reserved for human citizen scientists clicking away at galaxies, climate records or snapshots from the Serengeti. This landscape is completely different from when I was a graduate student just a decade ago – then, the machines just weren’t quite up to scratch in many cases. Now they’re starting to outperform people in more and more tasks.

 

Rather than replacing citizen scientists, though, machines can help them – and it could not have come at a better time. Scientific experiments are flooding researchers with data: astronomers needed the help of the Internet to classify one million galaxies from an astronomical survey that took place in the 1990s and 2000s. Soon telescopes like the Large Synoptic Sky Telescope will give us images of billions of galaxies in addition to supernovae, asteroids and other strange things that go bump in the night.

 

How will astronomers be able to deal with all these data, many of which are time-sensitive? After all, if something goes “bump” and fades quickly, we’d want to try to study it more before it disappears forever. That’s where the machines can really help us: deep minds can scale up to process large data sets if we just give them sufficient processing power and memory.

 

But the machines still need help – our help! One of the biggest problems for deep neural nets is that they require large training sets, examples of data (say, images of galaxies) which have already been carefully and accurately classified. This is one way in which the citizen scientists will be able to contribute: train the machines by providing high-quality training sets so the machines can then go off and deal with the rest of the data.

There’s another way citizen scientists will be able to pitch in: by helping us identify the weird things out there we don’t know about yet, the proverbial Rumsfeldian “unknown unknowns.” Machines can struggle with noticing unusual or unexpected things, whereas humans excel at it.

 

Having the citizen scientists help the machines spot these unexpected things in the data would complement the machines’ ability to churn through huge data sets. If a machine got confused by something, or just wanted some extra feedback, it could kick the object back to a human for help, and then update itself to deal with similar things in the future. This could find applications not just in astrophysics, but in many other fields of science, from surveys of the sea floor to archives in museums, and the detectors of particle accelerators.

 

So envision a future where a smart system for analyzing large data sets diverts some small percentage of the data to human citizen scientists to help train the machines. The machines then go through the data, occasionally spinning off some more objects to the humans to improve machine performance as time goes on. If the machines then encounter something odd or unexpected, they pass it on to the citizen scientists for evaluation. Thus, humans and machines will form a true collaboration: citizen science cyborgs.

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A new view of the X-ray sky

A new view of the X-ray sky | Amazing Science | Scoop.it

Scientists at the Max Planck Institute for Extraterrestrial Physics (MPE) have revisited the all-sky survey carried out by the ROSAT satellite, to create a new image of the sky at X-ray wavelengths. Along with this a revised and extended version of the catalogue of bright and faint point-like sources will be released. The now published "2RXS catalogue" provides the deepest and cleanest X-ray all-sky survey to date, which will only be superseded with the launch of the next generation X-ray survey satellite, eROSITA, currently being completed at MPE.

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Gamma-ray bursts may place first lower bound on the cosmological constant

Gamma-ray bursts may place first lower bound on the cosmological constant | Amazing Science | Scoop.it

Sometimes when a star collapses into a supernova, it releases an intense, narrow beam of gamma rays. Gamma-ray bursts often last just a few seconds, but during that time they can release as much energy as the Sun will produce in its entire lifetime, making gamma-ray bursts the most powerful explosions ever observed in the universe. They are so intense that, if pointed at the Earth from even the most distant edge of our galaxy, they could easily cause a mass extinction, possibly obliterating all life on the planet. It's thought that a gamma-ray burst may have caused the Ordovician extinction around 440 million years ago, which wiped out 85% of all species at the time.

Clearly, the farther away a planet is from gamma-ray bursts, the better its chances of harboring advanced forms of life. In a new paper, scientists have shown that the gamma-ray burst risk to life favors a universe where all objects (like planets and gamma-ray bursts) are relatively far apart. And the main factor that tells how far apart everything is in the universe—or in other words, how things are spreading out and moving away from each other—is dark energy or the cosmological constant.

 

One of the biggest unanswered questions in cosmology is why does the cosmological constant have the particular value that scientists observe? Einstein initially devised the cosmological constant to be like an "anti-gravity" force, so that a larger value means that the universe is expanding very rapidly and objects are being pushed farther apart from each other. A smaller value means that the universe itself is smaller and objects are somewhat closer together.

 

Currently, the value of the cosmological constant is estimated to be about 10-123. Researchers have placed upper bounds on this value (it can't be more than 10-120 or else galaxies and other structures could not form because their matter could not have gotten close enough together). But so far, no research has been able to place a lower bound on the value.

 

By showing that the chances of advanced life existing is extremely small when planets are close to gamma-ray bursts, the new study makes an argument for placing the first lower bounds on the value of the cosmological constant. The scientists estimate that, when the value gets below 10-124, the number of protective "halos" of space (regions where planets stand a chance of avoiding gamma-ray bursts for long periods of time) sharply decreases. In other words, it would be pretty unlikely for humans to exist if the value were smaller than this number.

 

"We have found a lower limit on the cosmological constant," coauthor Tsvi Piran at The Hebrew University in Jerusalem told Phys.org. "As you know it is very small, 10-123. If it is so small, then why not zero? Zero is a 'round' number and one can look for a basic law of physics that will force the cosmological constant to vanish. Additionally, why not a negative value?"

 

By showing that the cosmological constant is very unlikely to be zero or negative, and much more likely to be close to its observed value, the results may help explain where this value comes from.

"This is important as it gives clues to the question of what is the origin of this constant," Piran said. "It is generally believed that the value of the cosmological constant is determined by some quantum process, and understanding its relevant range is important to have a clue on its origin."

 

The full analysis is more complicated, as the researchers had to account for other factors, such as the age of the universe—it can't be too young nor too old for advanced life. It can't be too old because planets need to orbit around a hydrogen-burning star like our Sun, which is young enough that it has not yet reached the end of its lifetime. But the universe also can't be too young because a galaxy (where protective halos reside) must have time to undergo chemical evolution to produce metal elements. A high metallicity decreases the odds of having a nearby gamma-ray burst, since the stars that cause these bursts have relatively low metal concentrations.

 

It's not surprising that Earth seems to occupy a favorable point in the researchers' simulations: a place with minimal exposure to gamma-ray bursts, and at a time with many hydrogen-burning stars like the Sun, along with a high average metallicity. This special place and time may help researchers search for other possible locations of life in the universe.

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Longest-lasting stellar eclipse: Three-and-a-half year eclipses in binary system

Longest-lasting stellar eclipse: Three-and-a-half year eclipses in binary system | Amazing Science | Scoop.it

Astronomers have discovered an unnamed pair of stars that sets a new record for both the longest duration stellar eclipse (3.5 years) and longest period between eclipses (69 years) in a binary system.


Imagine living on a world where, every 69 years, the sun disappears in a near-total eclipse that lasts for three and a half years. That is just what happens in an unnamed binary star system nearly 10,000 light years from Earth. The newly discovered system, known only by its astronomical catalog number TYC 2505-672-1, sets a new record for both the longest duration stellar eclipse and the longest period between eclipses in a binary system.


Discovery of the system's extraordinary properties was made by a team of astronomers from Vanderbilt and Harvard with the assistance of colleagues at Lehigh, Ohio State and Pennsylvania State universities, Las Cumbres Observatory Global Telescope Network and the American Association of Variable Star Observers and is described in a paper accepted for publication in the Astronomical Journal.


"It's the longest duration stellar eclipse and the longest orbit for an eclipsing binary ever found...by far," said the paper's first author Vanderbilt doctoral student Joey Rodriguez. The previous record holder is Epsilon Aurigae, a giant star that is eclipsed by its companion every 27 years for periods ranging from 640 to 730 days.


"Epsilon Aurigae is much closer -- about 2,200 light years from Earth -- and brighter, which has allowed astronomers to study it extensively," said Rodriguez. The leading explanation is that Epsilon Aurigae consists of a yellow giant star orbited by a normal star slightly bigger than the sun embedded in a thick disk of dust and gas oriented nearly edge on when viewed from Earth.


"One of the great challenges in astronomy is that some of the most important phenomena occur on astronomical timescales, yet astronomers are generally limited to much shorter human timescales," said co-author Keivan Stassun, professor of physics and astronomy at Vanderbilt. "Here we have a rare opportunity to study a phenomenon that plays out over many decades and provides a window into the types of environments around stars that could represent planetary building blocks at the very end of a star system's life."


Two unique astronomical resources made the discovery possible: observations by the American Association of Variable Star Observers (AAVSO) network and the Digital Access to a Sky Century @ Harvard (DASCH) program.

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Shafique Miraj Aman's curator insight, March 2, 5:44 AM

69 years(not a sexual innuendo) of having no natural light. now that actually sounds fun