Astronomers discover 'hyper-starburst' galaxy

A recently discovered galaxy is forming stars at an extraordinary pace. Astronomers have shown that, compared to the Milky Way, which forms roughly one Sun-sized star per year, stars in the galaxy SPT 0346-32 are forming at a rate of about 4,500 times the mass of the Sun every year—one of the highest rates seen.

The finding presents an opportunity to study one of the mysteries behind star formation, according to one of the study’s co-authors at the University of Illinois.  

Researchers used NASA's Chandra X-ray Observatory and other telescopes to reveal the phenomenon occurring some 12.7 billion light years from Earth. Given the great distance, the observed images are from a critical and early stage in the evolution of galaxies—only about a billion years after the Big Bang.

After astronomers discovered the galaxy with the National Science Foundation's South Pole Telescope (SPT), they observed it with several space and other ground-based telescopes. Data from the international Atacama Large Millimeter/submillimeter Array (ALMA) previously revealed extremely bright infrared emission, suggesting that the galaxy is undergoing a tremendous burst of star birth.

However, an alternative explanation remained: Was much of the infrared emission instead caused by a rapidly growing supermassive black hole at the galaxy's center? Gas falling towards the black hole would become much hotter and brighter, causing surrounding dust and gas to glow in infrared light. To explore this possibility, researchers used NASA’s Chandra X-ray Observatory and Commonwealth Scientific and Industrial Research Organisation’s Australia Telescope Compact Array, a radio telescope.

No X-rays or radio waves were detected, so astronomers were able to rule out a black hole being responsible for most of the bright infrared light.

"We now know that this galaxy doesn't have a gorging black hole, but instead is shining brightly with the light from newborn stars," said Jingzhe Ma of the University of Florida in Gainesville, Florida, who led the new study. "This gives us information about how galaxies and the stars within them evolve during some of the earliest times in the Universe."

Said co-author Anthony Gonzalez, also of the University of Florida, "Astronomers call galaxies with lots of star formation 'starburst' galaxies. That term doesn’t seem to do this galaxy justice, so we are calling it a 'hyper-starburst' galaxy."

The high rate of star formation implies that a large reservoir of cool gas in the galaxy is being converted into stars with unusually high efficiency. Astronomers hope that by studying more galaxies like SPT0346-52 they will learn more about the formation and growth of massive galaxies and the supermassive black holes at their centers.

"For decades, astronomers have known that supermassive black holes and the stars in their host galaxies grow together," said study co-author Joaquin Vieira, a professor of astronomy of the University of Illinois. "Exactly why they do this is still a mystery. SPT0346-52 is interesting because we have observed an incredible burst of stars forming, and yet found no evidence for a growing supermassive black hole. We would really like to study this galaxy in greater detail and understand what triggered the star formation and how that affects the growth of the black hole."

SPT0346-52 is part of a population of strong gravitationally-lensed galaxies discovered with the SPT. SPT0346-52 appears about six times brighter than it would without gravitational lensing, which enables astronomers to see more details than would otherwise be possible.

An interactive image, a podcast, and a video about the findings are available here.