The Universe’s Baby Boom
A new telescope will tell us how the first stars and galaxies were born.
- By Bruce Lieberman
- Air & Space magazine, August 2013
(Page 2 of 3)
During the observatory’s early science testing run in 2011 and 2012, Jacqueline Hodge from the Max-Planck Institute for Astronomy in Germany pinpointed the locations of more than 100 early starburst galaxies. Her team worked from a map made by the nearby Atacama Pathfinder Experiment (APEX), a single 12-meter-dish radio observatory, which identified 126 distant galaxies with blobs of light indicating star-forming regions. Using ALMA, Hodge found that many were multiple galaxies that were blurred together, and she identified their locations with 200 times more accuracy—using only a quarter of ALMA’s array. Once the entire array is online this fall, Hodge’s team plans to go back and increase the precision of their results even further.
Now astronomers can start to probe details within the galaxies. “We have a hard time understanding how a galaxy can literally produce that many stars,” Hodge says. “Some of these things are producing 3,000-solar-mass stars per year,” compared to a galaxy like the Milky Way, which today produces only a few sun-like stars annually. “Our computer models are straining to produce these types of galaxies.
“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.