Matthew Lehnert on the oldest known object in the universe
In late 2010, astronomers reported the discovery of the oldest known object in the universe thus far. It’s a very small galaxy, said Matthew Lehnert, lead astronomer of the study. He spoke with us from his office at the Paris Observatory.
Matthew Lehnert: The galaxy itself, since it’s so early in the age of the universe – literally only 600 million years after the Big Bang, the explosion that created the space and the time in which we exist – means that it really doesn’t have time to accumulate a lot of gas and hence form a lot of stars.
The galaxy, called UDFy-38135539, is in the direction of the constellation Fornax in the southern sky. The stars in this oldest known galaxy, because they’re young, are very massive and bright, said Lehnert.
Matthew Lehnert: And by measuring that light, we actually can tell how far away it is, or alternatively, how long ago this object existed. Because you have to remember that distance and time in the universe are virtually one and the same. That means that as we look at things that are very far away, we’re also seeing them as they were a long time ago.
Lehnert said study of the first galaxies reveals what the early universe was like, as the first simple atoms of hydrogen and helium formed after the Big Bang.
Matthew Lehnert: So as these first galaxies formed, they began to emit light that actually turned the universe back into it’s previous earlier state of being ionized , as we call it. In other words, instead of a soup of hydrogen and helium atoms, it became a soup of protons and electrons again. And because of that, we can say that the universe went through a dramatic phase change. It means that these first galaxies, like the one that we observed with this red shift, in the early universe, actually created a change in the entire structure of the universe.
He described what the galaxy is like.
Matthew Lehnert: The galaxy itself is actually very small in size, diameter. It’s about 1/20 the size of our own Milky Way galaxy. But the number of stars in it is something like 1/100 to 1/1000 the size of our own galaxy, the Milky Way. And the reason I give you a range of values for these numbers is because we’re actually highly uncertain. Because the galaxy’s so faint, it’s hard to actually get very tight constraints on the size and how many stars are in the galaxy.
He said that because the galaxy is formed in the very early universe, it’s also very young
Matthew Lehnert : Our galaxy, for example, at least in the solar neighborhood, meaning the area around our own sun, is about 10 billion years old, maybe more like nine. But it’s of that order. Those are the oldest stars near the sun. But this galaxy is probably more like 50 million or 100 million years old. That means that most of the stars in this galaxy are not only young, but they also are very massive. That means that they emit a lot of light. It’s one of the reasons we can actually see the galaxy at such a great distance. It’s actually bright compared to the Milky Way, even though the Milky Way has a lot more stars in it. So that made it visible. Having said all that, of course, it’s still an extremely faint galaxy, which means it’s very, very difficult to study it and learn a lot about it.
This galaxy is one of the first ever formed, said Lehnert.
Matthew Lehnert:It’s observed so long ago in time that we’re really pushing back to the first real galaxies. Now this is a mater of semantics in a way, right? There must have been smaller galaxies that are actually forming at the same time as this galaxy formed. There probably were smaller galaxies that formed even earlier. So what you call ‘first,’ is perhaps a bit of a definition of what first is.