A galaxy so far away that we see practically at the edge of the visible universe, has been seen to behave like a full-fledged galaxy: observations show it is spinning, spinning in a similar way to our own Milky Way, although we see it as it were. Only 500 million years after the Big Bang!
The galaxy is called MACS1149-JD1 – or just JD1 for short – and its light took about 13.3 billion years to reach us. Given that the universe is only 13.8 billion years old, we see this galaxy as it was when it was already very young.
It’s so far away that it’s usually too faint to be seen, but it lies behind a very massive cluster of galaxies called MACSJ1149.5 + 223. This cluster is only about 5 billion light-years away from us, much closer to us than JD1, and that’s lucky: The massive gravity of the galaxies embedded in the cluster acts like a lens, bending and amplifying the light from JD1, making it bright enough to see. It also enlarges the JD1’s image, allowing us to see it in more detail, just as a lens does.
JD1 has been studied before, and surprisingly one paper showed that stars in the galaxy were already forming only 250 million years after the universe itself was born. In another study, astronomers used the Atacama Large Millimeter/ Submillimeter Array, or ALMA, to observe the galaxy with a wavelength of about 88 microns, and saw light from oxygen atoms glow brightly. Oxygen is formed inside massive stars and is expelled because they explode at the end of their lives, so some of these stars have already been born, old and dead by the time we see this galaxy, which is Fabulous.
New work expands on those notes [link to paper]. Astronomers used ALMA to monitor oxygen in JD1 at 88 microns again, but this time it took nearly 10 hours of observations, compared to just two hours in the previous hours. The longer the observation, the more light the telescope collects, making the structure and details easier to see. Although it is still somewhat low resolution – we are talking about a galaxy very Far away, after all – they can see structures that are about 1,000 light-years wide in one dinar.
What they found is a clear indication that some of the light from the oxygen is being emitted by a substance moving toward us, and some by a substance moving away from us. This is a good indication of rotation: an object that is half rotating is moving towards us and half is moving away, causing a Doppler shift in its light. It’s this shift that astronomers have seen (after calculating the massive redshift of the galaxy itself, we’ve been swept away by the expansion of the universe).
The galaxy is small, with a diameter of about 3000 light-years, which is not very surprising. At the time, galaxies in the universe were just beginning to form through accretion of gas, so they didn’t have time to grow as massive as our Milky Way, for example, which is about 120,000 light-years across. It is also much less massive as well, about 650 million times more massive than the Sun. For comparison, the Milky Way is 1,000 times larger than JD1.
A rotating galaxy rotates at a rate that depends on its mass, because this is what determines gravity, and gravity is what keeps stars in their orbits. JD1 rotates at a rate of just under 50 kilometers per second, compared to more than 200 in the Milky Way. So this is a galaxy that is still young and developing in all respects, but it is already showing signs of puberty. Think of it as an awkward teen.
All the physical modeling done by the astronomers showed that JD1 is consistent with being a disk galaxy, such as a spiral galaxy, with stars formed about 300 million years ago, which is in good agreement with what was seen in previous work using a different method for obtaining the age stellate. It also means that even at such a young age it is possible for galaxies to form themselves into disks, which is a very impressive result.
All this makes JD1 the most distant galaxy ever seen with signs of rotation, as well as the most distant galaxy in which we can detect structure and motion. Everything that was found corresponds to models of how galaxies behaved in the early universe, too, which is encouraging. This means that we are probably on the right track to understanding what the universe looked like when he was a young child. Riddles are fun science, but the occasional hint that we’re doing the right thing is nice, too.
It’s something of a fan
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