ALMA finds large numbers of massive galaxies in the early universe
Imagine that you’re on an open field in the middle of the night. In the distance is the edge of a dark forest. Using your binoculars, you see dozens of fireflies buzzing around between the trees. Great, that tells you what kind of animals live out there, right?
But then you pick up your night goggles. In addition to visible light, they are also sensitive to the body heat of living organisms. Now, you suddenly see other animals, too: mice, hedgehogs, birds, and even the occasional swine or deer. These animals are both larger and more numerous than the fireflies.
Astronomers found themselves in a similar situation. They used the Hubble Space Telescope to study the dark, distant universe. Sure enough, they detected many remote galaxies. These galaxies poured out a lot of visible light because they were forming huge numbers of new stars. Such galaxies are known as starburst galaxies.
But now, ALMA has studied the same part of the sky. Not at the visible wavelengths that Hubble can see, but at millimeter and submillimeter wavelengths. It’s as if astronomer put their night goggles on. And to their surprise, they found many large, dark galaxies that Hubble could not see.
The newly detected galaxies are also producing large numbers of new stars, although not as much as the starburst galaxies that Hubble found. However, in the case of the ALMA galaxies, the starlight is absorbed by massive amounts of dust. As a result, the galaxies can only be seen by telescopes that observe at infrared or submillimeter wavelengths.
The galaxies studied by Hubble and ALMA are extremely far away. Their light takes some 10 billion years to reach Earth. Therefore, we see them as they were ten billion years ago, when the universe was still relatively young. Over time, the massive, dark ALMA galaxies will probably evolve into the large, heavy-weight elliptical galaxies that we can see all around us today.
But there’s a puzzle. Astronomers didn’t expect that, ten billion years ago, there would already be so many of these large, massive galaxies. Apparently, they form much faster and in greater numbers than anyone imagined. So maybe we have to rethink our ideas about the origin and early evolution of galaxies. That’s why this discovery is so important.
The massive, dark galaxies that ALMA found are located in the so-called CANDELS field – a region in the sky that has been studied in much detail. The Hubble Space Telescope discovered many distant starburst galaxies in the CANDELS field. Later, the Spitzer Space Telescope, which observes infrared radiation, detected 63 objects that were nog visible in the Hubble images. However, the Spitzer images were not detailed enough to reveal their true nature. ALMA, with its superb sensitivity and eagle-eyed vision, has now discovered submillimeter radiation from 39 of these 63 objects. They turn out to be large, massive, dark galaxies. They produce about a hundred times more new stars than our own Milky Way galaxy, but most of the starlight is absorbed by dust. Based on the number that ALMA has detected, astronomers estimate that there may be over 20 million of these dark, massive galaxies across the whole sky.
The ALMA observations of the distant dark, massive galaxies were carried out by Tao Wang of the University of Tokyo (Japan) and a large international group of colleagues. The discovery was important enough to end up in Nature, a prestigious professional weekly magazine on all topics of scientific research.Check this in ALMA site