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Clues to Universe’s Evolution Provided by ‘Hyper-Starburst’ Galaxy

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A galaxy that was recently discovered by a group of astronomers led by graduate student Jingzhe Ma from the University of Florida using NASA’s Chandra X-Ray Observatory, is undergoing an extraordinary boom of stellar construction.

The galaxy is known as SPT 0346‐52 and is 12.7 billion light years from Earth. The observations are done about a billion years after the Big Bang, which is seen as a critical stage in the evolution of galaxies.

SPT 0346‐52 was discovered by astronomers using the National Science Foundation’s South Pole Telescope. Later observations were done with with space and ground-based telescopes. Extremely bright infrared emission was revealed by data from the NSF / ESO Atacama Large Millimeter / submillimeter Array in Chile. This suggests that the galaxy is undergoing a tremendous burst of star birth.

There is however an alternative explanation. The huge quantity of infrared emission could be caused by a rapidly growing supermassive black hole at the galaxy’s center. If this were the case, gas falling towards the black hole would become much brighter and hotter. This would in turn cause surrounding gas and dust to glow in infrared light. Astronomers used CSIRO’s Australia Telescope Compact Array, a radio telescope, and NASA’s Chandra X‐ray Observatory to explore this possibility.

As radio waves or X‐rays were not detected, astronomers ruled out the theory that a black hole was responsible for most of the bright infrared light.

Ma explained that as this galaxy does not have a gorging black hole, it is shining brightly with the light from newborn stars. This provides information about how galaxies and the stars within them evolved during the earliest time in the universe.

Stars in SPT0346-52 are forming at one of the highest rates seen in a galaxy – about 4,500 times the mass of the Sun every year. A galaxy like the Milky Way only forms about one solar mass of new stars per year.

Anthony Gonzalez, a UF professor of astronomy and co-author of the study, notes that astronomers call galaxies with lots of star formation ‘starburst’ galaxies. He adds that as that term does not do this galaxy justice, they decided to call it a ‘hyper-starburst’ galaxy.

The fact that the star formation happens at such a high rate probable means that a large pool of cool gas in the galaxy is being converted into stars with abnormally high efficiency.

By studying more galaxies such as SPT0346‐52, astronomers hope they will learn more about the growth and formation of massive galaxies and the supermassive black holes that are normally at their centers.

Joaquin Vieira of the University of Illinois at Urbana Champaign and co-author of the study, notes that although they have known for decades that supermassive black holes and the stars in their host galaxies grow together, it is unclear why they do this. She adds that SPT0346-52 is interesting in the sense that astronomers have observed an incredible burst of stars forming, but have not found any evidence for a growing supermassive black hole. They would like to understand what triggered the star formation and how that influences the growth of the black hole by studying this galaxy in more detail.

SPT0346‐52 is a fragment of a population of strong gravitationally lensed galaxies that were discovered with the SPT and it seems about six times brighter than it would without gravitational lensing. This allows astronomers to see more details than would otherwise be likely.

Image credits : UFL .edu
Image credits : UFL .edu

In the simulation shown, the distorted galaxy is the result of a collision between two galaxies, followed by them merging. Astronomers believe such a merger could be the reason why SPT0346-52 has such a flourishing stellar construction.

As shown by the bright region in the center of the simulation, gas near the center of the merged galaxy is compressed once the two galaxies collide. This produces a burst of new stars.

The composite inset shows various wavelengths as recorded by different telescopes:

  • Green – short wavelength infrared data from Hubble
  • Red – infrared light from Spitzer at longer wavelengths
  • Magenta – infrared data from ALMA at even longer wavelengths
  • Blue – X-ray data from Chandra

The gravity of an intervening galaxy causes the light from SPT0346-52 to be magnified and distorted. This produces the three elongated images in the ALMA data located near the middle of the image.

Although the Spitzer or Hubble data does not show SPT0346-52 directly, the gravitational lensing caused by the intervening galaxy is detected.

Chandra did not detect any X-rays that might have signaled the presence of a black hole that is growing. This is shown by the fact that there is no blue at the center of the image.

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