MAMBO-9: Most Distant Dusty, Star-Forming Galaxy Spotted Hiding 'In Plain Sight'

Dusty galaxies are considered the most intense star nurseries in the universe, forming stars with a rate of up to a few thousand times the mass of our sun per year. By comparison, the Milky Way’s star-forming rate is just three solar masses per year.

Astronomers believe that such dusty galaxies are vital to the evolution of the universe, but it is not exactly easy to find them because their light is often hidden by clouds of dust.

One such galaxy is MAMBO-9, which one of a new paper’s co-authors, Manuel Aravena, detected 10 years ago using the Max-Planck Millimeter BOlometer (MAMBO) instrument on the IRAM 30-meter telescope and the Plateau de Bure Interferometer in France. Unfortunately, the instruments were not sensitive enough to actually reveal the distance of the galaxy. Further, because other telescopes were unable to detect it, they doubted whether the galaxy was even real.

In the new study published in The Astrophysical Journal, however, researchers describe finally spotting the light of MAMBO-9, the most distant dusty, star-forming galaxy ever observed without the help of a gravitational lens. Typically, the galaxies closer to us act as a gravitational lens by bending the light from more distant galaxies. However, while it does make it easier to spot distant objects, it also makes it more difficult to determine the details.

"These galaxies tend to hide in plain sight," lead author Caitlin Casey of the University of Texas at Austin said.

Thankfully, the Atacama Large Millimeter/submillimeter Array's (ALMA) sensitivity detected MAMBO-9 without a lens, meaning that they had an unobstructed view of MAMBO-9.

This allowed them to actually determine its distance and even measure its mass.

“The total mass of gas and dust in the galaxy is enormous: ten times more than all the stars in the Milky Way.This means that it has yet to build most of its stars,” Casey said.

Based on observations, MAMBO-9 appears to have two parts and is currently in the process of merging. As MAMBO-9 was discovered during an ALMA survey to find dusty galaxies in the early universe, Casey is hoping to find even more of such galaxies so that they can better understand how they formed early in the universe, how common they really are, and why they are so dusty.

“Observations with new and more capable technology can produce unexpected findings like MAMBO-9,” Joe Pesce of National Radio Astronomy Observatory and ALMA said. “While it is challenging to explain such a massive galaxy so early in the history of the universe, discoveries like this allow astronomers to develop an improved understanding of, and ask ever more questions about, the universe .”

Interestingly, the light from MAMBO-9 actually traveled 13 billion light-years before reaching ALMA's antennas. This means that what we are seeing is actually what it looked like in the past. Today, it is likely that MAMBO-9 has already grown more massive and contains a hundred times more stars than our Milky Way.