Astronomers have spotted the earliest known spiral galaxy, dating to just three billion years after the Big Bang.
(The Hubble image of BX442 hints at neat spiral arms and at top left, an orbiting dwarf galaxy. Credit: Nature)
“Theories of galaxy formation held that the Universe was still too chaotic a place to allow such a perfectly formed or “grand-design” spiral to form. It should take far longer for gravity to bring matter into thin, neat discs.”
“But a team reporting in Nature says the galaxy BX442 got the gravitational “kick” it needed to form a spiral from a smaller ‘dwarf galaxy’ orbiting it. They first spotted BX442 as the one and only spiral-looking object in a survey of 300 galaxies carried out by the Hubble space telescope, when they were shocked to see what looked to be a spiral galaxy.”
”’What we’ve learned when we look at galaxies at that epoch is that they’re very dynamically hot,’ explained lead author of the study David Law from the University of Toronto’s Dunlap Institute for Astronomy and Astrophysics.”
“‘Even though we see some discs existing at that time, they’re very thick and puffy, whereas the Milky Way has an… amount of random motion only about a tenth or so the amount of ordered rotation, giving rise to a very thin disc.’”
(At first this result seemed amazingly unexpected, since I’ve studied the ways galaxies evolve over the history of the universe for my Ph.D. thesis. The bottom line is that, in the era when BX442 existed as we see it now, the Universe was a terribly violent place: galaxies collided frequently, whereas spiral structure is a pretty delicate thing that’s easily disrupted. How could BX442 possibly exist at z ~ 2? It turns out, the authors of the Nature paper argue that what they think is a dwarf galaxy near it “excited” the spiral structure, which is a short-lived phenomenon; otherwise, they say, it would have the typically “clumpy” appearance of disk galaxies in that era. Still, it is at least a technological feat that we can now resolve disks at such early times. Future telescope facilities should allow us to push that resolution back to even higher redshifts. The question is then: when did the first spiral galaxy form? -JCB)
Astronomy news, recent research results, and pretty pictures from the media along with context, commentary, and explanations for folks who dig this sort of thing. Written by a quasi-professional astronomer affiliated with the University of Texas at Austin.