Further evidence that some monster black holes killed star formation in their galaxies has been revealed in a study that dates back 12.5 billion years to the early universe.
Stars form when cold clouds of molecular hydrogen gas collapse, fragment and condense. The process of star formation continues in the Milky Wayas is the case in many other galaxies, but some, such as large elliptical galaxiesseem to have ended their star formation billions of years ago.
Astronomers have suspected that the feedback, in the form of powerful radiation emitted by matter swirling around a a supermassive black hole in the center of a galaxy, can heat the molecular gas in this galaxy and prevent it from collapsing to form stars. It could even blow this gas entirely out of a galaxy. These galaxies are described as “red and dead” because once star formation stops, the only stars left are long-lived cool red stars.
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Although there is ample circumstantial evidence that comments from black holes can suppress star formation, astronomers are still waiting for conclusive observations of this process and trying to understand how it happens. Now, a research team has shown that galaxies in the early universe that stopped forming stars have black holes which are more active than those of galaxies which are still forming stars.
The team, led by Kei Ito of SOKENDAI (the Graduate University for Advanced Studies) in Japan, scoured the Cosmic Evolution Survey (COSMOS) archives for distant galaxies to test the hypothesis that active black holes and red and dead galaxies are connected. COSMOS
involves some of the largest and most powerful telescopes, such as the Subaru Telescope in Hawaii, the Very large painting radio telescope in New Mexico, the The Hubble Space Telescope and the European Space Agency XMM-Newton X-Ray Telescope.
Ito’s team scanned galaxies as they existed 9.5 to 12.5 billion years ago, with the oldest galaxies forming only 1.3 billion years after the big Bang. The researchers were looking for X-ray and radio signals from active black holes, but because these signals are quite weak, they had to combine, or “stack,” X-ray and radio images from several of these distant galaxies to improve the signal-to-noise ratio, then average the combined data.
The team found that red, dead galaxies had stronger black hole activity than galaxies that were still forming stars during the same period.
Although the new findings, published in April in The Astrophysical Journal, do not prove that black hole feedback stifles star formation, they strengthen the hypothesis by connecting active black holes to red, dead galaxies. Scientists hope NASA James Webb Space Telescope will provide additional evidence after science operations begin this summer.
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