The Universe’s Baby Boom

A new telescope will tell us how the first stars and galaxies were born.

The Atacama Large Millimeter/Submillimeter Array in Chile is tuned to see radiation emitted long ago when the first galaxies formed. (ALMA Observatory)
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“I think [ALMA] is poised to change the field,” Hodge says.

When Vieira’s team looked for dusty starburst galaxies, they were able to take advantage of a natural effect that boosted the resolution even further. The galaxies they observed with ALMA had been magnified—sometimes more than 20 times—by the gravitational effects of large masses, like other galaxies in the foreground, in an effect known as gravitational lensing.

Furthermore, Vieira’s team was able to determine redshifts for nearly all the galaxies it observed, from which they could infer the galaxy’s age and distance from Earth. “It just blew my mind, because we have been trying to do this for so long with so many different instruments,” says Vieira. His team had attempted to get images and redshift measurements from the Hubble, Spitzer, and Herschel space telescopes, and ground-based telescopes in Hawaii and Chile.

With precise redshift measurements for these early galaxies, astronomers can start to piece together the chronology of matter formation in the early universe. “We had not determined any redshifts yet, and then we just got on our laps all this data,” Vieira says. “And it was gorgeous and there was the answer. It was an amazing feeling…. It was immediately clear that [ALMA] was orders of magnitude more powerful than anything else we’ve been using before.”

When Vieira’s team returns later this year after ALMA is fully operational, Vieira says they expect to get better resolution than the Hubble. With that kind of power, ALMA will be able to get distance measurements not just to a galaxy, but to distinct regions within it as well. Astronomers will be able to build three-dimensional images of galaxies billions of light-years away.

When and how heavy elements and molecules arose are important questions for Avi Loeb, a cosmologist at Harvard University and the Harvard-Smithsonian Center for Astrophysics. Clouds of molecular gas in early galaxies cooled and eventually collapsed into stars like our sun, and this process occurs more efficiently in the presence of heavy elements than in their absence. Astronomers want to understand this peak era of star formation because this is when the universe changed from a uniform sea almost entirely composed of hydrogen and helium gas to a growing web of galaxies rich with the chemical elements that would eventually form planets and, at least on Earth, life.

How far back in time ALMA will be able to look will be limited by when dusty galaxies existed in cosmic history. It’s the dust emissions that ALMA detects, and Hubble observations suggest that as we look closer to the beginning of the universe—going from when re-ionization was complete back to the ignition of those first stars—the universe gets progressively freer of dust.

“Now, ALMA may tell us a different story, and that would be very interesting,” says Caltech astronomer Richard Ellis. “I think there’s a lot of hype about ALMA that is unproven yet, but it’s realistic to be optimistic. We know so little about early galaxies that the basic argument is ‘Let’s go and have a look and see what we see.’ ”

One of the next tests for ALMA will be to see if it can detect smaller, dimmer galaxies, which are predicted to be far more common within the first billion years of the Big Bang, rather than the monster starburst galaxies discovered by Vieira and others last year. “Much of the re-ionization is done by feeble little things, and so we would dearly like to get details of their properties,” Ellis says.

Ellis is on a team led by University of Edinburgh astronomer James Dunlop that will use ALMA to image 100 galaxies within the Hubble Ultra Deep Field. Last January at the annual meeting of the American Astronomical Society in Long Beach, California, Ellis’ team announced that, within Hubble’s infrared data, they had tentatively found a handful of galaxies that existed when the universe was just 570 million years old, and one that existed at just 370 million years, making it the most distant and earliest object ever discovered.

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