So, You’re Still Interested in Astronomy?
 The Way Our Galaxy Formed?

The wonderful thing about astronomy is that there’s always something new to learn.

I spotted an article in Science Magazine recently that touched on a recent discovery made by Astronomers who managed to observe a stably rotating disk galaxy just 1.5 billion years after the Big Bang. Why is this big news? Well, when the universe was just 1.5 billion years old, it had already stabilized enough to form a miniature Milky Way. And though tiny, this galaxy is significant for what it represents: one of the earliest known rotating disk galaxies — and the best indicator yet for how galaxies like the Milky Way formed.

Early MILKY WAYS

Marcel Neeleman (Max Planck Institute for Astronomy, Germany) and his colleagues maintained observations on galaxy, DLA0817g, nicknamed the Wolfe Disk after late astronomer Arthur M. Wolfe. They used the Atacama Large Millimeter/submillimeter Array (ALMA) and the Hubble Space Telescope to obtain images as small as 4,200 light-years across in a galaxy whose light has traveled for 12.5 billion years to reach Earth.

That data – combined with the Hubble images – provided solid evidence that the emissions researchers are tracking coincides with a rotating disk of dust, gas, including stars within the galaxy.

The formation of a stable disk galaxy in the early universe does away with some theories on galaxy formation, which suggested that secreting gas would be too hot to settle into an infant disk until much later on. Likewise, major mergers between galaxies would too chaotic to settle into an orderly disk.

Instead, the Wolfe Disk’s existence provides evidence that the universe’s first galaxies grew in a manner that lets infalling gas remain cool and relatively stable. Indeed, computer simulations have show that this so-called cold-mode accretion was important in the universe’s early years, and while it doesn’t rule out mergers altogether, those mergers would have been much smaller than those coming later in the evolutionary process.

AND WHERE THERE’S ONE . . .?

The Wolfe Disk isn’t the first disk galaxy to be discovered in the early universe. In 2015, astronomers looked back over 11 billion years to discover what appeared to be a massive, rotating galaxy. And in 2017, ALMA observations of galaxies that formed only 800 million years after the Big Bang offered further evidence of rotation. But Wolfe is the first galaxy where the observations are on a firm-enough footing to rein in theoretical scenarios.

Said Alfred Tiley of the University of Western Australia. “Neeleman and colleagues’ results constitute some of the first observational evidence for the existence of cold gas disks in massive galaxies very soon after the Big Bang. Now, the trick will be to find more — hopefully, a lot more — like it, and see if this galaxy is representative of disk galaxies in general.”

I guess we shall see.