New from Space: Simulations and X-Rays Point to Dark Matter

center_universe2The cosmic hunt for dark matter has been turning up some interesting clues of late. And during the month of June, two key hints came along that might provide answers; specifically simulations that look at the “local Universe” from the Big Bang to the present day and recent studies involving galaxy clusters. In both cases, the observations made point towards the existence of Dark Matter – the mysterious substance believed to make up 85 per cent of the mass of the Universe.

In the former case, the clues are the result of new supercomputer simulations that show the evolution of our “local Universe” from the Big Bang to the present day. Physicists at Durham University, who are leading the research, say their simulations could improve understanding of dark matter due to the fact that they believe that clumps of the mysterious substance – or halos – emerged from the early Universe, trapping intergalactic gas and thereby becoming the birthplaces of galaxies.

universe_expansionCosmological theory predicts that our own cosmic neighborhood should be teeming with millions of small halos, but only a few dozen small galaxies have been observed around the Milky Way. Professor Carlos Frenk, Director of Durham University’s Institute for Computational Cosmology, said:

I’ve been losing sleep over this for the last 30 years… Dark matter is the key to everything we know about galaxies, but we still don’t know its exact nature. Understanding how galaxies formed holds the key to the dark matter mystery… We know there can’t be a galaxy in every halo. The question is: ‘Why not?’.

The Durham researchers believe their simulations answer this question, showing how and why millions of halos around our galaxy and neighboring Andromeda failed to produce galaxies. They say the gas that would have made the galaxy was sterilized by the heat from the first stars that formed in the Universe and was prevented from cooling and turning into stars. However, a few halos managed to bypass this cosmic furnace by growing early and fast enough to hold on to their gas and eventually form galaxies.

dark_matterThe findings were presented at the Royal Astronomical Society’s National Astronomy Meeting in Portsmouth on Thursday, June 26. The work was funded by the UK’s Science and Technology Facilities Council (STFC) and the European Research Council. Professor Frenk, who received the Royal Astronomical Society’s top award, the Gold Medal for Astronomy, added:

We have learned that most dark matter halos are quite different from the ‘chosen few’ that are lit up by starlight. Thanks to our simulations we know that if our theories of dark matter are correct then the Universe around us should be full of halos that failed to make a galaxy. Perhaps astronomers will one day figure out a way to find them.

Lead researcher Dr Till Sawala, in the Institute for Computational Cosmology, at Durham University, said the research was the first to simulate the evolution of our “Local Group” of galaxies, including the Milky Way, Andromeda, their satellites and several isolated small galaxies, in its entirety. Dr Sawala said:

What we’ve seen in our simulations is a cosmic own goal. We already knew that the first generation of stars emitted intense radiation, heating intergalactic gas to temperatures hotter than the surface of the sun. After that, the gas is so hot that further star formation gets a lot more difficult, leaving halos with little chance to form galaxies. We were able to show that the cosmic heating was not simply a lottery with a few lucky winners. Instead, it was a rigorous selection process and only halos that grew fast enough were fit for galaxy formation.

darkmatter1The close-up look at the Local Group is part of the larger EAGLE project currently being undertaken by cosmologists at Durham University and the University of Leiden in the Netherlands. EAGLE is one of the first attempts to simulate from the beginning the formation of galaxies in a representative volume of the Universe. By peering into the virtual Universe, the researchers find galaxies that look remarkably like our own, surrounded by countless dark matter halos, only a small fraction of which contain galaxies.

The research is part of a program being conducted by the Virgo Consortium for supercomputer simulations, an international collaboration led by Durham University with partners in the UK, Germany, Holland, China and Canada. The new results on the Local Group involve, in addition to Durham University researchers, collaborators in the Universities of Victoria (Canada), Leiden (Holland), Antwerp (Belgium) and the Max Planck Institute for Astrophysics (Germany).

ESO2In the latter case, astronomers using ESA and NASA high-energy observatories have discovered another possible hint by studying galaxy clusters, the largest cosmic assemblies of matter bound together by gravity. Galaxy clusters not only contain hundreds of galaxies, but also a huge amount of hot gas filling the space between them. The gas is mainly hydrogen and, at over 10 million degrees celsius, is hot enough to emit X-rays. Traces of other elements contribute additional X-ray ‘lines’ at specific wavelengths.

Examining observations by ESA’s XMM-Newton and NASA’s Chandra spaceborne telescopes of these characteristic lines in 73 galaxy clusters, astronomers stumbled on an intriguing faint line at a wavelength where none had been seen before. The astronomers suggest that the emission may be created by the decay of an exotic type of subatomic particle known as a ‘sterile neutrino’, which is predicted but not yet detected.

dark_matter_blackholeOrdinary neutrinos are very low-mass particles that interact only rarely with matter via the so-called weak nuclear force as well as via gravity. Sterile neutrinos are thought to interact with ordinary matter through gravity alone, making them a possible candidate as dark matter. As Dr Esra Bulbul – from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, USA, and lead author of the paper discussing the results – put it:

If this strange signal had been caused by a known element present in the gas, it should have left other signals in the X-ray light at other well-known wavelengths, but none of these were recorded. So we had to look for an explanation beyond the realm of known, ordinary matter… If the interpretation of our new observations is correct, at least part of the dark matter in galaxy clusters could consist of sterile neutrinos.

The surveyed galaxy clusters lie at a wide range of distances, from more than a hundred million light-years to a few billion light-years away. The mysterious, faint signal was found by combining multiple observations of the clusters, as well as in an individual image of the Perseus cluster, a massive structure in our cosmic neighborhood.

The supermassive black hole at the center of the Milky Way galaxy.The implications of this discovery may be far-reaching, but the researchers are being cautious. Further observations with XMM-Newton, Chandra and other high-energy telescopes of more clusters are needed before the connection to dark matter can be confirmed. Norbert Schartel, ESA’s XMM-Newton Project Scientist, commented:

The discovery of these curious X-rays was possible thanks to the large XMM-Newton archive, and to the observatory’s ability to collect lots of X-rays at different wavelengths, leading to this previously undiscovered line. It would be extremely exciting to confirm that XMM-Newton helped us find the first direct sign of dark matter. We aren’t quite there yet, but we’re certainly going to learn a lot about the content of our bizarre Universe while getting there.

Much like the Higgs Boson, the existence of Dark Matter was first theorized as a way of explaining how the universe appears to have mass that we cannot see. But by looking at indirect evidence, such as the gravitational influence it has on the movements and appearance of other objects in the Universe, scientists hope to one day confirm its existence. Beyond that, there is the mystery of “Dark Energy”, the hypothetical form of energy that permeates all of space and is believed to be behind accelerations in the expansion of the universe.

As with the discovery of the Higgs Boson and the Standard Model of particle physics, detecting these two invisible forces will at last confirm that the Big Bang and Cosmological theory are scientific fact – and not just working theories. When that happens, the dream of humanity finally being able to understand the universe (at both the atomic and macro level) may finally become a reality!

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The Future is Here: “Terminator-style” Liquid Metal Treatment

t1000_1For ideal physical rehab, it might be necessary to go a little “cyborg”. That’s the reasoning a Chinese biomedical firm used to develop a new method of repairing damaged nerve endings. Borrowing a page from Terminator 2, their new treatment calls for the use of liquid metal to transmit nerve signals across the gap created in severed nerves. The work, they say, raises the prospect of new treatment methods for nerve damage and injuries.

Granted, it’s not quite on par with the liquid-metal-skinned cyborgs from the future, but it is a futuristic way of improving on current methods of nerve rehab that could prevent long-term disabilities. When peripheral nerves are severed, the loss of function leads to atrophy of the effected muscles, a dramatic change in quality of life and, in many cases, a shorter life expectancy. Despite decades of research, nobody has come up with an effective way to reconnect them yet.

nerveVarious techniques exist to sew the ends back together or to graft nerves into the gap that is created between severed ends. And the success of these techniques depends on the ability of the nerve ends to grow back and knit together. But given that nerves grow at the rate of one mm per day, it can take a significant amount of time (sometimes years) to reconnect. And during this time, the muscles can degrade beyond repair and lead to long-term disability.

As a result, neurosurgeons have long hoped for a way to keep muscles active while the nerves regrow. One possibility is to electrically connect the severed ends so that the signals from the brain can still get through; but up until now, an effective means of making this happen has remained elusive. For some time, biomedical engineers have been eyeing the liquid metal alloy gallium-indium-selenium for some time as a possible solution – a material that is liquid at body temperature and thought to be entirely benign.

Liquid metal nervesBut now, a biomedical research team led by Jing Liu of Tsinghua University in Beijing claims they’ve reconnected severed nerves using liquid metal for the first time. They claim that the metal’s electrical properties could help preserve the function of nerves while they regenerate. Using sciatic nerves connected to a calf muscle, which were taken from bullfrogs, they’ve managed to carry out a series of experiments that prove that the technique is viable.

Using these bullfrog nerves, they applied a pulse to one end and measured the signal that reached the calf muscle, which contracted with each pulse. They then cut the sciatic nerve and placed each of the severed ends in a capillary filled either with liquid metal or with Ringer’s solution – a solution of several salts designed to mimic the properties of body fluids. They then re-applied the pulses and measured how they propagated across the gap.

liquid metal nerves_1The results are interesting, and Jing’s team claim that the pulses that passed through the Ringer’s solution tended to degrade severely. By contrast, the pulses passed easily through the liquid metal. As they put it in their research report:

The measured electroneurographic signal from the transected bullfrog’s sciatic nerve reconnected by the liquid metal after the electrical stimulation was close to that from the intact sciatic nerve.

What’s more, since liquid metal clearly shows up in x-rays, it can be easily removed from the body when it is no longer needed using a microsyringe. All of this has allowed Jing and colleagues to speculate about the possibility of future treatments. Their goal is to make special conduits for reconnecting severed nerves that contain liquid metal to preserve electrical conduction and therefore muscle function, but also containing growth factor to promote nerve regeneration.

future_medicineNaturally, there are still many challenges and unresolved questions which must be resolved before this can become a viable treatment option. For example, how much of the muscle function can be preserved? Can the liquid metal somehow interfere with or prevent regeneration? And how safe is liquid metal inside the body – especially if it leaks? These are questions that Jing and others will hope to answer in the near future, starting with animal models and possibly later with humans..


What Would Hyperspace Really Look Like?

hyperspaceRemember those iconic scenes in Star Wars when the Millennium Falcon made the jump to hyperspace? Remember how cool it looked when the star field stretched out and then the ships blasted off? And of course, every episode of Star Trek was punctuated by a jump to warp, where once again, the background stars seemed to stretch out and then hurl on past the Enterprise.

Yes, for generations, this is how people envisioned Faster-Than-Light travel. Whether it consisted of rainbow-colored streaks shooting past, or a quick distortion followed by a long, blue tunnel of bright light, these perceptions have become a staple of science fiction. But one has to wonder… in a universe where FTL was really possible, would it really look anything like this?

hyperspace3Using Einstein’s Theory of Relativity, four students from the University of Leicester produced a paper in January of last year where they theorized what a jump to light-speed would really look like. Based on the theory that the speed of light is the absolute threshold at which elementary particles can move in this universe, the four students – Riley Connors, Katie Dexter, Joshua Argyle, and Cameron Scoular – claimed that a ship that can exceed c would have an interesting view.

In short, they claim that the crew wouldn’t see star lines stretching out past the ship during the jump to hyperspace, but would actually see a central disc of bright light. This is due to the Doppler effect, specifically the Doppler blue shift, that results in the wavelength of electromagnetic radiation, including visible light, shortening as the source of the light moves towards the observer.

Hyperspace. Nuff said?
Hyperspace. Nuff said?

As the ship made the jump to hyperspace, the wavelength of the light from the stars would shift out of the visible spectrum into the X-ray range. Meanwhile, Cosmic Background Radiation (CBR), which is thermal radiation that is spread fairly uniformly across the universe and is thought to be left over from the Big Bang, would shift into the visible spectrum, appearing to the crew as a central disc of bright light.

What’s more, even a ship like the Millennium Falcon would require additional energy to overcome the pressure exerted from the intense X-rays from stars that would push the ship back and cause it to slow down. The students say the pressure exerted on the ship would be comparable to that felt at the bottom of the Pacific Ocean.

red-shift-03However, if the ship in question took its time getting up to speeds in excess of the speed of light, there would be some interesting visual effects. Given how light and the color spectrum works, as a ship continued to speed up, the stars in front of the ship would experience blueshift (shifting towards the blue end of the spectrum), while those behind it would experience redshift (shifting towards the red end).

But the moment the threshold of light speed was passed, background radiation would be all that was left to see. And once that happened, the crew would experience some rather intense radiation exposure. As Connors put it:

If the Millennium Falcon existed and really could travel that fast, sunglasses would certainly be advisable. On top of this, the ship would need something to protect the crew from harmful X-ray radiation.

And as Dexter suggested, referring to Disney’s purchase of Lucasfilm for a cool $4.05 billion: “Disney should take the physical implications of such high speed travel into account in their forthcoming films.” I won’t be holding my breath on that one. Somehow, star lines look so much cooler than a mottled, bright disc in the background, don’t you think?


News From The Center of the Galaxy!

sagittarius A_flareAt least once a day, the black hole that resides at the center of the Milky Way Galaxy – aka. Sagittarius A* – shoots out an x-ray flare. These flares range in luminosity and intensity, but are usually only on the magnitude of a few dozens times its normal output. However, back in February of 2012, astronomers using the Chandra X-Ray Observatory detected the brightest flare ever observed from the central black hole, measured at 150 times its normal output.

Located some 26,000 light years from Earth, Sagittarius A* emits X-rays on a regular basis, and no one is sure why. However, a group of researchers postulated that it may be the results of asteroids or planets that wander too close to the hole and are consumed. Essentially, they believe Sagittarius A* is taking in rocky objects, eating them up, and then shooting out x-rays as exhaust.

The supermassive black hole at the center of the Milky Way galaxy.According to Michael Nowak, a research scientist at MIT Kavli and co-author of a new paper in the Astrophysical Journal, a sudden increase in consumption might explain the flare. “Suddenly, for whatever reason, Sagittarius A* is eating a lot more,” he said. “One theory is that every so often, an asteroid gets close to the black hole, the black hole stretches and rips it to pieces, and eats the material and turns it into radiation, so you see these big flares.”

This is the standard procedure that astronomers use to detect black holes – i.e. by the light energy given off as they swallow nearby matter – since they are invisible to the naked eye. Not only are black holes notorious for consuming matter, even light and gravity, the very fabric of time and space, are consumed in their maws. However, through an x-ray telescope, the centers of galaxies can appear extremely bright, giving off massive amounts of energy as they devour their surroundings. As they age, they tend to slow down, consuming less and appearing fainter.

Another MIT alumnist, Frederick K. Baganoff, has been conducting observations on Sagittarius A* with the Chandra X-ray Observatory since 2003, and in that time he has noted some interesting things. For example, he calculated that, given the amount of gas in its surroundings, Sagittarius A* should be about a million times brighter than it is — a finding that suggested the black hole throws away most of the matter they would otherwise consume.

Or as he puts it: “Everyone has this picture of black holes as vacuum sweepers, that they suck up absolutely everything. But in this really low-accretion-rate state, they’re really finicky eaters, and for some reason they actually blow away most of the energy… We’re really studying the great escape, because most of the gas escapes, and that’s not what we expect.”

The physics that underlie this process are still a mystery, but researchers like Baganoff hope to learn more through more observation. In the end, the real pay off is that it will help us to understand the history of activity at the center of our Galaxy, a history which goes back billions of years and can tell us volumes about the formation of our Milky Way and even the universe itself.