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 Thirty Meter Telescope –“Next Generation in the Search for Extraterrestrial Life”

The Thirty Meter Telescope (TMT) – soon to be the world’s widest eye on space – has got the go-ahead for construction on the summit of Mauna Kea, Hawaii. Most of Mauna Kea is below sea level. When measured from its oceanic base, its height is 33,500 ft (10,200 m)—more than twice Mount Everest’s base-to-peak height. The sacred mountain is about one million years old –long past the most active shield stage of life hundreds of thousands of years ago–providing a stable platform for what will will be the world’s most advanced and capable ground-based optical, near-infrared, and mid-infrared observatory.

The TMT will integrate the latest innovations in precisions control, segmented mirror design, and adaptive optics. The giant eye will enable groundbreaking advances in a wide range of scientific areas, from the most distantreaches of the Universe to our own Solar System. TMT will allow astronomers to explore virtually every aspect of this picture, from inflation to exoplanets.

The resolution and sensitivity provided by its large aperture and adaptive optics systems, combined with a flexible and powerful suite of instruments, will enable astronomers to address many of the most fundamental questions ofthe coming decades.

One of the primary missions of the TMT will be the detection and analysis of life-bearing exo planets. The exoplanets that have so far been detected are gas giants like Jupiter and Neptune. They were found because their large mass noticeably perturbs the motion of the host star. Surprisingly, many are found very close to their host star. As the higher temperatures there would prevent such planets from forming, itseems that they must have migrated inward, after forming at greater distances. Most astronomers believe that smaller terrestrial planets exist, but these cannot be detected with present telescopes. The TMT will help answer such questions as are such planets common and can they survive the disruption that would result from migration of the massive planets? Do they have atmospheres like Earth?

via The Thirty Meter Telescope –“Next Generation in the Search for Extraterrestrial Life”.

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.

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.