Galaxy merger dilemma solved

Washington, April 21 (ANI): A long-standing dilemma about the mass of infrared bright merging galaxies has finally been solved by scientists at the Naval Research Laboratory (NRL).

Dr. Barry Rothberg along with Dr. Jacqueline Fischer used new data from the 8-meter Gemini-South telescope in Chile along with earlier results from the W. M. Keck-2 10-meter and University of Hawaii 2.2-meter telescopes in Hawaii and archival data from the Hubble Space Telescope, to solve the problem.

Galaxies in the Universe generally come in two shapes, spiral, like our own Milky Way, and elliptical, in which the stars move in random orbits.

The largest galaxies in the Universe are elliptical in shape and how they formed is central to our understanding how the Universe has evolved over the last 15 billion years.

The long-standing theory has been that spiral galaxies merge with each other forming most of the elliptical galaxies in the Universe.

Spiral galaxies contain significant amounts of cold hydrogen gas. When they merge, the beautiful spiral patterns are destroyed and the gas is converted into new stars and with it, large amounts of dust. The dust is heated by the young stars and radiates energy at infrared wavelengths.

Until recently scientists thought that these infrared bright merging galaxies were not massive enough to be the precursors of most elliptical galaxies in the Universe.

The conventional method of measuring mass in dusty IR-bright galaxies uses near-infrared light, which can penetrate dust, to measure the random motions of old-stars.

The larger the random motions, the more mass is present. When spirals merge, gas from both galaxies forms a central rotating disk which then forms new stars.

These young stars outshine the old stars at near-infrared wavelengths making it appear as if the old stars have less random motion. Rothberg and Fischer instead observed the random motions of old stars at shorter wavelengths effectively using the dust to block the light from the young stars.

Their new results showed that the old stars in merging galaxies have large random motions, which means they will eventually become very massive elliptical galaxies.

The new research has been published in the Astrophysical Journal. (ANI)

Awesome power of supermassive black holes revealed

Washington, April 17 (ANI): Nottingham University researchers have shed new light on the super destructive capacity of black holes.

For the study, Asa Bluck in the School of Physics and Astronomy and colleagues, used images of unprecedented depth and resolution from the Hubble Space Telescope and the Chandra X-Ray Observatory to detect black holes in distant galaxies.

Scientists looked for galaxies emitting high levels of radiation and x-rays – a classic signature of black holes devouring gas and dust through accretion, or attracting matter gravitationally.

As this matter swirls around the event horizon of a black hole it heats up and radiates energy – as an accretion disc.

In supermassive black holes this radiation can reach huge proportions, emitting X-ray radiation in far greater quantities then is emitted by the rest of the objects in the galaxy combined – meaning that the black hole ”shines” far brighter than the entire galaxy it lies at the heart of.

In fact, the amount of energy released is sufficient to strip the galaxy of gas at least 25 times over.

Results have also demonstrated that the vast majority of the X-ray radiation present in the universe is produced in these accretion discs surrounding supermassive black holes, with a small proportion produced by all other objects, including galaxies and neutron stars.

The accretions discs surrounding supermassive black holes produce so much energy that they heat up the cold gases lying at the heart of massive galaxies.

The accretion disc shines across all wavelengths – from radio waves to gamma waves.

This speeds up the random motions of the gas, making it rise in temperature and pushing it away from the galactic centre, where it becomes less dense.

Gas needs to be cold and dense to collapse under gravity to form new stars, this resulting hot, low-density material must cool down before gravity will take effect – a process which would take longer than the age of the universe to achieve.

Old stars are therefore left to die out with no new stars replacing them, leaving the galaxy to grow dark and die.

And by pushing gas away from the galactic centre, the accretion disc starves the supermassive black hole of new material to devour, leading to its eventual demise.

Asa Bluck, a PhD student at the University and a Fellow of the Royal Astronomical Society, said: “It”s thought that black holes form inside their host galaxies and grow in proportion to them, forming an accretion disc which will eventually destroy the host. In this sense they can be described as viral in nature.

“Massive galaxies are in the minority in our visible universe – about one in a thousand galaxies is thought to be massive, but it may be much less. And at least a third of these have supermassive black holes at their centre. That”s why it”s so interesting that this type of black hole produces most of the X-ray light in the universe. They are the minority but they dominate energy output.”

The study, a collaboration between researchers at The University of Nottingham and Imperial College London, was presented at the Royal Astronomical Society National Astronomy Meeting in Glasgow. (ANI)