Astrophysics: A glimpse inside a magnetar.

A neutron star resembles a giant atomic nucleus, with 1–2 times the Sun’s mass packed into a ball about 20 kilometres across. Its gravity is so strong that a projectile would need to be launched at about half the speed of light to escape from its surface. Extreme density, pressure, temperature, magnetism and relativistic gravity make these objects fascinating but challenging to study. Surprising observations of spin-down irregularities in one intensely magnetized neutron star, reported by Archibald et al.1 on page 591 of this issue, offer clues about exotic processes occurring deep inside these objects.

The basic structure of a neutron star is generally agreed on. It has a crust about 1 km thick, in which nuclei are arranged in a crystal lattice immersed in a ‘sea’ of electrons. Near the surface, the nuclei are plain iron, but the pressure and density increase rapidly with depth, so that the nuclei become increasingly bloated and neutron-rich. At moderate depth, neutrons ‘drip’ out of the nuclei, forming a neutral liquid between the lattice nuclei. At the base of the crust, the bloated nuclei merge. Below this lies pure nuclear fluid, more than 200 trillion times denser than liquid water.

via Astrophysics: A glimpse inside a magnetar : Nature : Nature Publishing Group.

Galaxy formation: Cosmic dawn

For one sleepless week in early September 2009, Garth Illingworth and his team had the early Universe all to themselves. At NASA’s request, Illingworth, Rychard Bouwens and Pascal Oesch had just spent the previous week staring into their computer screens at the University of California, Santa Cruz, scanning through hundreds of black-and-white portraits of faint galaxies recorded in a multi-day time exposure by a newly installed infrared camera on the Hubble Space Telescope. NASA simply wanted the three astronomers to preview the images and make sure that the camera was working correctly, before the agency released the data more widely.

via Galaxy formation: Cosmic dawn : Nature News & Comment.

Observable Light in the Universe –Blazars Offer a Measuring Tool

If all the light emitted by all galaxies in the observable universe at all wavelengths during all of cosmic history were known, it would clue astronomers about the entire history of galaxy formation and evolution, and provide insights to key aspects of the expansion history of the universe. But measuring this light — known as extragalactic background light (EBL) — is no simple task, complicated by the fact that Earth is lodged inside a bright solar system and the Milky Way, a very bright galaxy, making it enormously difficult for ground-based and space-based telescopes to reliably measure EBL. Furthermore, current galaxy surveys being used to estimate EBL could very well be missing information from faint galaxies and other sources.

A team of astronomers has come up with a solution that ingeniously overcomes the technical challenges of measuring EBL. They propose in a paper published May 24 in The Astrophysical Journal that one answer to the problem of measuring EBL lies in measuring the attenuation — or weakening — of very high-energy gamma rays from distant “blazars,” which are supermassive black holes in the centers of galaxies.

via Observable Light in the Universe –Blazars Offer a Measuring Tool.

The Weekend Image : Andromeda Galaxy’s Supermassive Black Hole

The Hubble Space Telescope image below centers on the 100-million-solar-mass black hole at the hub of the neighboring spiral galaxy M31, or the Andromeda galaxy, the only galaxy outside the Milky Way visible to the naked eye and the only other giant galaxy in the local group. This is the sharpest visible-light image ever made of the nucleus of an external galaxy. The event horizon, the closest region around the black hole where light can still escape, is too small to be seen, but it lies near the middle of a compact cluster of blue stars at the center of the image.

The compact cluster of blue stars is surrounded by the larger “double nucleus” of M31, discovered with the Hubble Space Telescope in 1992. The double nucleus is actually an elliptical ring of old reddish stars in orbit around the black hole but more distant than the blue stars. When the stars are at the farthest point in their orbit they move slower, like cars on a crowded freeway. This gives the illusion of a second nucleus.

The blue stars surrounding the black hole are no more than 200 million years old, and therefore must have formed near the black hole in an abrupt burst of star formation. Massive blue stars are so short-lived that they would not have enough time to migrate to the black hole if they were formed elsewhere.

Astronomers are trying to understand how apparently young stars were formed so deep inside the black hole’s gravitational grip and how they survive in an extreme environment.

via The Weekend Image : Andromeda Galaxy’s Supermassive Black Hole.

Giant Elliptical Galaxy Harbors Largest Known Black Hole in Universe

The black hole at the center of the super giant elliptical galaxy M87 in cluster Virgo fifty million light-years away is the most massive black hole for which a precise mass has been measured -6.6 billion solar masses. Orbiting the galaxy is an abnormally large population of about 12,000 globular clusters, compared to 150-200 globular clusters orbiting the Milky Way. The team theorized that the M87 black hole grew to its massive size by merging with several other black holes. M87 is the largest, most massive galaxy in the nearby universe, and is thought to have been formed by the merging of 100 or so smaller galaxies. The M87 black hole’s large size and relative proximity, astronomers think that it could be the first black hole that they could actually “see.”

In 2011, using the Frederick C. Gillett Gemini Telescope on Mauna Kea, Hawaii, a team of astronomers calculated the black hole’s mass, which is vastly larger than the black hole in the center of the Milky Way, which is about 4 million solar masses. The black hole’s event horizon, 20 billion km across “could swallow our solar system whole.”

via Giant Elliptical Galaxy Harbors Largest Known Black Hole in Universe.

Hints of lightweight dark matter get even stronger.

A strange light is shining near the centre of the Milky Way, and evidence is mounting that it is the spark of lightweight dark matter meeting a violent end. At the same time, a suite of sensitive detectors deep underground is seeing hints of similar particles.

Dark matter is thought to make up roughly 80 per cent of the matter in the universe. But aside from its gravitational tug on regular matter, the substance has proven tough to detect, and many of its fundamental properties remain unknown.

The leading theoretical candidates for dark matter are weakly interacting massive particles (WIMPs). It’s thought these particles annihilate when they meet, producing a shower of radiation, including gamma rays. Launched in 2008, NASA’s Fermi space telescope has been scanning for excess gamma rays emanating from the centre of our galaxy, where dark matter should be concentrated.

Last year scientists ruled out a possible Fermi signal at 130 gigaelectronvolts (GeV) as dark matter’s smoking gun. But there is another: In 2010, physicist Dan Hooper at Fermilab in Batavia, Illinois, and colleagues reported a possible hint from the space telescope of dark matter particles with a mass of about 10 GeV.

via Hints of lightweight dark matter get even stronger – space – 10 May 2013 – New Scientist.

A ‘Fifth Force’ May Alter Gravity at Cosmic Scales

Radical new research is attempting to characterize the properties of a fifth force that disrupts the predictions general relativity makes outside our own galaxy, on cosmic-length scales. University of Pennsylvania astrophysicist Bhuvnesh Jain, says the nature of gravity is the question of a lifetime. As scientists have been able to see farther and deeper into the universe, the laws of gravity have been revealed to be under the influence of an unexplained force.

Two branches of theories have sprung up, each trying to fill its gaps in a different way. One branch — dark energy — suggests that the vacuum of space has an energy associated with it and that energy causes the observed acceleration. The other falls under the umbrella of “scalar-tensor” gravity theories, which effectively posits a fifth force (beyond gravity, electromagnetism and the strong and weak nuclear forces) that alters gravity on cosmologically large scales.

“These two possibilities are both radical in their own way,” Jain said. “One is saying that general relativity is correct, but we have this strange new form of energy. The other is saying we don’t have a new form of energy, but gravity is not described by general relativity everywhere.”

Jain’s research is focused on the latter possibility; he is attempting to characterize the properties of this fifth force that disrupts the predictions general relativity makes outside our own galaxy, on cosmic length scales.

via A ‘Fifth Force’ May Alter Gravity at Cosmic Scales.

The Milky Way’s Violent Core –“Was It the Site of an Ancient Collision of Black Holes?”

There is growing evidence that several million years ago the galactic center was the site of violent cosmic events. A pair of assistant professors – Kelly Holley-Bockelmann at Vanderbilt and Tamara Bogdanović at Georgia Institute of Technology – have come up with an explanation that fits these “forensic” clues, suggesting how a single event – a violent collision and merger between the galactic black hole and an intermediate-sized black hole in one of the small “satellite galaxies” that circle the Milky Way – could have produced the features that point to a more violent past for the galactic core.

The most dramatic of these extraordinary clues are the Fermi bubbles.In 2010, NASA’s Fermi Gamma-ray Space Telescope unveiled a previously unseen structure centered in the Milky Way –two gamma-ray-emitting bubbles that extend 25,000 light-years north and south of the galactic center that spans 50,000 light-years and may be the remnant of an eruption from a supersized black hole at the center of our galaxy.

The structure spans more than half of the visible sky, from the constellation Virgo to the constellation Grus, and it may be millions of years old. “We don’t fully understand their nature or origin,” said Doug Finkbeiner, an astronomer at the Harvard-Smithsonian Center for Astrophysics, who first recognized the feature by processing publicly available data from Fermi’s Large Area Telescope (LAT). The LAT is the most sensitive and highest-resolution gamma-ray detector ever launched. Gamma rays are the highest-energy form of light.

via The Milky Way’s Violent Core –“Was It the Site of an Ancient Collision of Black Holes?”.

Does Antimatter Fall Up or Down?

The atoms that make up ordinary matter fall down, so do antimatter atoms fall up? Do they experience gravity the same way as ordinary atoms, or is there such a thing as antigravity?

These questions have long intrigued physicists, says Joel Fajans of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), because “in the unlikely event that antimatter falls upwards, we’d have to fundamentally revise our view of physics and rethink how the universe works.”

So far, all the evidence that gravity is the same for matter and antimatter is indirect, so Fajans and his colleague Jonathan Wurtele, both staff scientists with Berkeley Lab’s Accelerator and Fusion Research Division and professors of physics at the University of California at Berkeley – as well as leading members of CERN’s international ALPHA experiment – decided to use their ongoing antihydrogen research to tackle the question directly. If gravity’s interaction with anti-atoms is unexpectedly strong, they realized, the anomaly would be noticeable in ALPHA’s existing data on 434 anti-atoms.

The first results, which measured the ratio of antihydrogen’s unknown gravitational mass to its known inertial mass, did not settle the matter. Far from it. If an antihydrogen atom falls downward, its gravitational mass is no more than 110 times greater than its inertial mass. If it falls upward, its gravitational mass is at most 65 times greater.

What the results do show is that measuring antimatter gravity is possible, using an experimental method that points toward much greater precision in future. They describe their technique in the April 30, 2013 edition of Nature Communications.

How to measure a falling anti-atom

ALPHA creates antihydrogen atoms by uniting single antiprotons with single positrons (antielectrons), holding them in a strong magnetic trap. When the magnets are turned off, the anti-atoms soon touch the ordinary matter of the trap’s walls and annihilate in flashes of energy, pinpointing when and where they hit. In principle, if the experimenters knew an anti-atom’s precise location and velocity when the trap is turned off, all they’d have to do is measure how long it takes to fall to the wall.

ALPHA’s magnetic fields don’t turn off instantly, however; almost 30-thousandths of a second pass before the fields decay to near zero. Meanwhile flashes occur all over the trap walls at times and places that depend on the anti-atoms’ detailed but unknown initial locations, velocities, and energies.

Wurtele says, “Late-escaping particles have very low energy, so gravity’s influence is more apparent on them. But there were very few late escaping anti-atoms; only 23 of the 434 escaped after the field had been turned off for 20-thousandths of a second.”

Fajans and Wurtele worked with their ALPHA colleagues and with Berkeley Lab associates, UC Berkeley lecturer Andrew Charman and postdoc Andre Zhmoginov, to compare simulations with their data and separate gravity’s effects from those of magnetic field strength and particle energy. Much statistical uncertainty remained.

“Is there such a thing as antigravity? Based on free-fall tests so far, we can’t say yes or no, ” says Fajans. “This is the first word, however, not the last.”

ALPHA is being upgraded to ALPHA-2, and precision tests may be possible in one to five years. The anti-atoms will be laser-cooled to reduce their energy while still in the trap, and the magnetic fields will decay more slowly when the trap is turned off, increasing the number of low-energy events. Questions physicists and nonphysicists have been wondering about for more than 50 years will be subject to tests that are not only direct but could be definitive.

via Does Antimatter Fall Up or Down? « Berkeley Lab News Center.

“BX442” –The First Spiral Galaxy in the Universe?

It seems that, so far, it is: In July of 2012, astronomers observed a spiral galaxy in the early universe, billions of years before many other spiral galaxies formed while using the Hubble Space Telescope. They were taking pictures of about 300 very distant galaxies in the early universe to study their properties. This distant spiral galaxy they discovered  existed roughly three billion years after the Big Bang, and light from this part of the universe has been traveling to Earth for about 10.7 billion years.

“As you go back in time to the early universe, galaxies look really strange, clumpy and irregular, not symmetric,” said Alice Shapley, a UCLA associate professor of physics and astronomy, and co-author of the study. “The vast majority of old galaxies look like train wrecks. Our first thought was, why is this one so different, and so beautiful?”

“BX442 looks like a nearby galaxy, but in the early universe, galaxies were colliding together much more frequently,” she said. “Gas was raining in from the intergalactic medium and feeding stars that were being formed at a much more rapid rate than they are today; black holes grew at a much more rapid rate as well. The universe today is boring compared to this early time.”

Galaxies in today’s universe divide into various types, including spiral galaxies like our own Milky Way, which are rotating disks of stars and gas in which new stars form, and elliptical galaxies, which include older, redder stars moving in random directions. The mix of galaxy structures in the early universe is quite different, with a much greater diversity and larger fraction of irregular galaxies, Shapley said.

“The fact that this galaxy exists is astounding,” said David Law, lead author of the study and Dunlap Institute postdoctoral fellow at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics. “Current wisdom holds that such ‘grand-design’ spiral galaxies simply didn’t exist at such an early time in the history of the universe.” A ‘grand design’ galaxy has prominent, well-formed spiral arms.

The galaxy, which goes by the not very glamorous name of BX442, is quite large compared with other galaxies from this early time in the universe; only about 30 of the galaxies that Law and Shapley analyzed are as massive as this galaxy.

To gain deeper insight into their unique image of BX442, Law and Shapley went to the W.M. Keck Observatory atop Hawaii’s dormant Mauna Kea volcano and used a unique state-of-the-science instrument called the OSIRIS spectrograph, which was built by James Larkin, a UCLA professor of physics and astronomy. They studied spectra from some 3,600 locations in and around BX442, which provided valuable information that enabled them to determine that it actually is a rotating spiral galaxy — and not, for example, two galaxies that happened to line up in the image.

“We first thought this could just be an illusion, and that perhaps we were being led astray by the picture,” Shapley said. “What we found when we took the spectral image of this galaxy is that the spiral arms do belong to this galaxy. It wasn’t an illusion. We were blown away.” Law and Shapley also see some evidence of an enormous black hole at the center of the galaxy, which may play a role in the evolution of BX442.

Why does BX442 look like galaxies that are so common today but were so rare back then?

Law and Shapley say the answer may have to do with a companion dwarf galaxy, which the OSIRIS spectrograph reveals as a blob in the upper left portion of the image, and the gravitational interaction between them. Support for this idea is provided by a numerical simulation conducted by Charlotte Christensen, a postdoctoral scholar at the University of Arizona and a co-author of the research in Nature. Eventually the small galaxy is likely to merge into BX442, Shapley said.

Law, a former Hubble postdoctoral fellow at UCLA, and Shapley will continue to study BX442.

“We want to take pictures of this galaxy at other wavelengths,” Shapley said. “That will tell us what type of stars are in every location in the galaxy. We want to map the mixture of stars and gas in BX442.”

Shapley said that BX442 represents a link between early galaxies that are much more turbulent and the rotating spiral galaxies that we see around us. “Indeed, this galaxy may highlight the importance of merger interactions at any cosmic epoch in creating grand design spiral structure,” she said.

Studying BX442 is likely to help astronomers understand how spiral galaxies like the Milky Way form, Shapley concluded.

The image at the top of the page ian an artist’s conception of the farthest spiral galaxy ever seen; in a Hubble/Keck image (inset), the blob at upper left is a companion galaxy whose gravity may have sparked the spiral structure. Credit: (left) David Law; (right) Joe Bergeron, Dunlap Institute for Astronomy and Astrophysics

The Daily Galaxy via UCLA News and Nature.com

via “BX442” –The First Spiral Galaxy in the Universe?.