Distant Dust-Obscured Galaxy Is Forming Stars Much Faster Than Previously Thought

The universe we live in is an extremely dusty place. This "star stuff," as Carl Sagan once called it, is all around us and even within us — and it seeds the cosmos with the building blocks of life.

However, for astronomers trying to peer into the distant reaches of the universe, this dust is a bit of a problem — it blocks light emitted by faraway stars from reaching Earth, hiding from us what's really going on behind these clouds of dust.

A team of astronomers has now used the 50-meter Large Millimeter Telescope (LMT) perched on an extinct volcano in central Mexico to peer into a very distant dust-obscured galaxy. The observations, which were made possible due to the gravitational lensing effect caused by a foreground object, have revealed that this galaxy, named MACS071_Az9, is forming stars four times faster than previously thought.

The observations have been detailed in a study accepted for publication in the Astrophysical Journal.

"This very distant, relatively typical galaxy is known to us, and we knew it was forming stars, but we had no idea what its real star-formation rate was because there is so much dust surrounding it," study lead author Alexandra Pope, an astronomer at the University of Massachusetts Amherst, said in a statement. "Finding out that 75 percent of its star formation was obscured by dust is remarkable and intriguing. These observations clearly show that we have more to learn."

In order to get a clearer picture of these galaxies, the researchers made use of a phenomenon known as gravitational lensing.

Gravity, as Einstein’s theory of general relativity tells us, warps space-time. Occasionally, when the stars are aligned just right, this warping of the fabric of the universe results in a phenomenon known as gravitational lensing, wherein the strong gravitational field of a foreground object acts as a lens that “bends” light from an object in the background and allows scientists to catch a glimpse of what might otherwise have remained invisible.

"This technique offers a way to see things that are much fainter than your telescope can see," Pope said in the statement.

In this particular case, the lensing object was a massive "Frontier Fields" galaxy cluster named MACSJ0717.5+3745. Previous observations by the Hubble Space Telescope, which also utilized this gravitational lens, had suggested that stars in the background galaxy were forming at a rate of just four solar masses per year — much lower than the nearly 19 solar masses rate the new measurements revealed.

"We are not yet at the level of detecting all of the star formation going on, but we are getting better. One of the big goals for us is to push observations at longer wavelengths and to trace these very dusty galaxies at early epochs," Pope said. "We are pushing observations in this direction and the fact that Hubble found only one quarter of the star formation in this distant normal galaxy is a huge motivation for doing a lot more studies like this."