Researchers announce discovery that can change the concept of death of galaxies

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Accretion disk
Artist's rendition of a black hole with an orbiting companion star that exceeds its Roche limit. Mass from the companion star is drawn towards the black hole, forming an accretion disk. (Credits - Wikimedia Commons)

At American Astronomical Society‘s annual meeting in St. Louis, Missouri, Allison Kirkpatrick, assistant professor in physics and astronomy at the University of Kansas, will present the discovery of “cold quasars“. These are the galaxies with a huge amount of cold gas but can still produce new stars in spite of a quasar located at the centre. This breakthrough finding turns down many assumptions regarding the maturation of galaxies and it represents a phase in the life cycle of the galaxy which was not yet known.

A quasar which stands for quasi-stellar radio source can be described as a supermassive black hole on steroids. When gas falls toward a quasar at the galaxy’s centre it forms an accretion disk which has the potential to generate a huge amount of electromagnetic energy that has luminosity, hundred times more than a normal galaxy. It has been thought till now, that when a quasar forms, it signals the end of the galaxy’s ability to form new stars.

Kirkpatrick remarked that the gas which is accreting on the black hole gets heated and it forms X-rays. The light wavelength is a direct correspondence of the amount of heat. When something generates X-rays, then it is one of the hottest things in the universe. Humans, on the other hand, produce infrared light. After the accretion of the gas on the black hole, it moves at relativistic speeds and thus forms a magnetic field around gas. Similar to solar flares, there can be materials shooting off from the black hole. This essentially cuts off the gas supply in the galaxy, as a result, it loses the ability to form stars.

However, in the survey conducted by Kirkpatrick, nearly 10 percent of the galaxies with accreting black holes had a supply of cold gas remaining even after this phase and formed new stars. This is highly surprising and these are very unique objects. Out of this, a further 10 percent is even more unexpected. These are blue sources which resemble the end stages of a supermassive black hole. They are evolving to passive elliptical galaxy yet have a huge amount of cold gas in them. These are called cold quasars.

Kirkpatrick said that these galaxies are very rare and they have been observed in the transition period right before the star formation in the galaxy is over. These objects were first identified in the Sloan Digital Sky  – the detailed map of the universe. They were surveyed with the help of XMM Newton Telescope and Herschel Space Telescope. Next up, Kirkpatrick wants to determine if this occurs to every galaxy or a specific group of galaxies.

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