If you want your pet black hole to be visible, you must feed it regularly. Only when a black hole gorges on a steady diet of gas or other matter does it shine. The disk of matter that orbits it heats up and emits large amounts of light, especially in X-rays. If you have one of the supermassive black holes at the centers of galaxies, feeding it matter can create one of the brightest objects in the Universe.
But the smaller ones should also be pretty visible. And while astronomers expect and have observed black holes comparable in mass to stars, their numbers are fewer than expected, even after decades of searching. Perhaps, as a new paper suggests, this is because many black holes are hidden by an opaque, donut-shaped disk of matter.
J. M. Corral-Santana and colleagues based this hypothesis on a detailed study of a relatively faint, fluctuating X-ray source in the Milky Way. Their observations in X-ray and visible light revealed the signs of a binary system: an ordinary star in orbit around a black hole, similar to other systems, but with some key differences. For one, the star and black hole were so close together that the orbital period of the system was only 2.8 hours. For another, the matter being drawn off the star was obscuring the black hole when viewed from Earth. The authors hypothesized that many other black holes may be similarly hidden, and future searches should take that possibility into account.
Stellar-mass black holes are the remnants of the cores of stars which exploded in supernovae and are at least 20 times the mass of the Sun. Black holes in this mass range have been discovered in binary systems, where their companion is an ordinary star. The transfer of mass from the companion onto the black hole creates an accretion disk: a hot, rapidly rotating platter that emits a great deal of X-ray light. The first black hole discovered, Cygnus X-1, was found through these emissions.
However, in nearly 50 years of X-ray observations, only about 50 black holes candidates have been known in the Milky Way, of which only 18 are confirmed. None of them exhibit eclipses, where the companion star or accretion disk block the X-ray emission. That's a somewhat surprising result, as it may imply we're only identifying systems we see from a privileged angle, one where our telescopes peer "down" onto the system. Since a bright black hole system that undergoes eclipses was identified in the M33 (Triangulum) galaxy, astronomers know it does happen.
Steel beams are pretty uniformly strong, but they're all run of the mill, literally. If you start 3D-printing custom beams for the exact purpose they're intended to serve though, you've got a regular space-age material on your hands. It's lighter than steel and orders of magnitude stronger.
The process, developed byYong Mao of the University of Nottingham, UK and colleagues, isn't just the product of one innovation, but rather a whole bunch of them wrapped up into one bundle. First, you start out withF a hollow beam and you test it with the load it needs to bear. When it inevitably fails, you use some sophisticated software to analyze that sucker and 3D print an internal fractal structure to provide support, kind of like what's inside your bones.
Then lather, rinse, and repeat. With each iteration of ever-smaller fractal innards, the beam can gain strength by the order of magnitude, with practically negligible weight gain. Third generation beams, about as far as we can hope to go with current tech, are 10,000 times stronger than steel.
There is one big limitation to how strong you can get with this stuff however, and it all depends on printer fidelity. Since these sorts of beams are specifically designed, there's not much extra support to carry your load, so if the mesh isn't perfect, you could be in trouble. As 3D printers get better however, imperfections won't be a problem on the larger scales, and more and more iterations will be possible, making for structures that are both incredibly strong and incredibly light. Now if only they could figure out how to 3D print some new bones for us.
New technique could give conventional immunoassays a run for their money
Carbon-nanotube transistors could be used to detect minute quantities of disease biomarkers, such as the proteins implicated in prostate cancer, according to new experiments by researchers in the US. The technique could rival conventional methods when it comes to sensitivity, cost and speed.
Conventional techniques to detect proteins are typically based on some form of "immunoassay", with the most famous of these being enzyme-linked immunosorbent assay (ELISA). This technique involves introducing an enzyme-modified antibody protein to an unknown amount of target molecule or protein, known as an antigen, and allowing them to bind together. Unreacted antibodies are washed away, leaving behind only antibody–antigen pairs.
The reaction can usually be detected by a colour change in the solution or by a fluorescent signal. The degree of colour change or fluorescence depends upon the number of enzyme-modified antibodies present, which in turn depends on the initial concentration of antigen in the sample.
Although such tests are routinely used in hospitals and clinics, they are quite long, taking several days or even weeks to complete. They are also costly, complicated to perform and can only detect single proteins at a time.
"Our new nanotube sensors are relatively simple compared to these ELISA tests," team member Mitchell Lerner, at the University of Pennsylvania, told physicsworld.com. "Detection occurs in just minutes, not days, and even at the laboratory scale, the cost of an array of 2000 such sensors is roughly $50 or 2.5 cents per sensor."
More importantly still, the sensors are much more sensitive to the target proteins in question. Indeed the Pennsylvania researchers showed that they could detect a prostate-cancer biomarker called osteopontin (OPN) at 1 pg/mL, which is roughly 1000 times lower than that possible with clinical ELISA measurements.
Detecting Lyme disease: The team, which is led by A T Charlie Johnson of Penn's Department of Physics and Astronomy, made its nanotube sensors by attaching OPN-binding antibodies to carbon-nanotube transistors on a silicon chip. Many proteins in the body bind very strongly to specific target molecules or proteins, and OPN is no exception. When the chip is immersed in a test sample, the OPN binds to the antibodies, something that changes the electronic characteristics of the transistor. Measuring the voltage and current through each device thus allows the researchers to accurately measure how much OPN there is in the sample.
Stealth cancer doesn't alert the immune system to its presence.
Peter Phillips's insight:
With this discovery there is the potential to develop a vaccine which switches on identifying proteins in the membrane of the cancer cell, making it vulnerable to the devil's own immune system. Not only does this research paint a more positive future for the endangered devil, it also has offers hope for new cancer treatments for our own species.
ABC Rural brings you specialist and comprehensive coverage of the imminent release of the Murray-Darling basin plan - with on the ground reaction from across four states and the breaking news on each day.
Free video course on Foundations of Modern Physics by Leonard Susskind of Stanford. This Stanford Continuing Studies course is a six-quarter sequence of classes exploring the essential theoretical foundations of modern physics.
This Stanford Continuing Studies course is a six-quarter sequence of classes exploring the essential theoretical foundations of modern physics. The topics covered in this course focus on classical mechanics, quantum mechanics, the general and special theories of relativity, electromagnatism, cosmology, black holes and statistical mechanics. While these courses build upon one another, each section of the course also stands on its own, and both individually and collectively they will allow the students to attain the "theoretical minnimum" for thinking intelligently about physics. Quantum theory governs the universe at its most basic level. In the first half of the 20th century physics was turned on its head by the radical discoveriies of Max Planck, Albert Einstein, Niels Bohr, Werner Heisenberg, and Erwin Schroedinger. An entire new logical and mathematical foundation - quantum mechanics - eventually replaced classical physics. This course explores the quantum world, including the particle theory of light, the Heisenberg Uncertainty Principle, and the Schroedinger Equation. The course is taught by Leonard Susskind, the Felix Bloch Professor of Physics at Stanford University.
Here is a comprehensive listing of all lectures from Dr. Susskind:
The 2013 Academy Awards were, as always, as much about making appearances as about making films, as red carpet watchers noted fashion trends and faux pas. Both Jessica Chastain and Naomi Watts wore Armani, although fortunately not the same dress. And Best Supporting Actress Anne Hathaway switched from Valentino to a controversial pale pink Prada at the last minute because her original dress looked too much like someone else's. Of course, no actress would be caught dead wearing the same style 2 years in a row. A new study of ancient beaded jewelry from a South African cave finds that ancient humans were no different, avoiding outdated styles as early as 75,000 years ago.
Personal ornaments, often in the form of beads worn as necklaces or bracelets, are considered by archaeologists as a key sign of sophisticated symbolic behavior, communicating either membership in a group or individual identity. Such ornaments are ubiquitous in so-called Upper Paleolithic sites in Europe beginning about 40,000 years ago, where they were made from many different materials—animal and human teeth, bone and ivory, stone, and mollusk shells—and often varied widely among regions and sites.
Even more ancient personal ornaments go back to at least 100,000 years ago in Africa and the Near East. But this earlier jewelry seems less variable and was nearly always made from mollusk shells. So some archaeologists have questioned whether these earlier ornaments played the same symbolic roles as the later ones, or even whether they were made by humans at all.
In a new study in press at the Journal of Human Evolution, a team led by archaeologist Marian Vanhaeren of the University of Bordeaux in France claims to have found evidence of a relatively sudden shift in the way that shell beads were strung. The beads were found at Blombos Cave in South Africa in archaeological layers dated between 75,000 and 72,000 years ago, during a time period marked by four distinct layers of artifacts called the Still Bay tradition. This tradition includes bone awls and sophisticated stone spear points and knives, as well as beads from jewelry: sixty-eight specimens of the southern African tick shell, Nassarius kraussianus, most found clustered together and thought to be part of individual necklaces or bracelets. All the shells are perforated with a single hole, and the team's microscopic studies—as well as experiments with shells of the same species collected near the site—have suggested that they were punctured with a finely tipped bone point.
Thea Tlsty, UCSF Professor of Pathology, explains the biology of cancer; that cancer arises primarily through damage to the genetic program of our cells, how this leads to uncontrolled growth and invasion, how cancer intrudes upon and destroys adjacent or distant tissues, and how the inner workings of the cancer cell function. Series: "UCSF Osher Mini Medical School for the Public" [1/2012]
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