Our models of how things in the universe are supposed to work have a bad habit of turning out completely wrong. Recently astronomers tossed a few more models in the garbage after discovering an enormous, ancient galaxy, they've described as "the monster" due to its size, age and the incredible rate at which it formed stars—over 1,000 times faster than the Milky Way. But the confusing thing is that one day it just stopped making stars altogether. And astronomers have no idea what caused the death of this strange cosmic monstrosity.
The technical name for this galaxy is XMM-2599. It was discovered by astronomers using the W. M. Keck Observatory's Multi-Object Spectrograph for Infrared Exploration, or MOSFIRE. Ben Forrest, postdoctoral researcher at UC Riverside, describes what makes this galaxy so strange and unique:
“Even before the universe was 2 billion years old, XMM-2599 had already formed a mass of more than 300 billion suns, making it an ultramassive galaxy. More remarkably, we show that XMM-2599 formed most of its stars in a huge frenzy when the universe was less than one billion years old, and then became inactive by the time the universe was only 1.8 billion years old.”
According to Gillian Wilson, a professor of physics and astronomy at UC Riverside, galaxies this old and this massive are predicted to exist by the numerical models, although rarely. The numerical models, however, predict that such galaxies should still be actively forming stars. The mysterious death of XMM-2599 throws a wrench into those models. Wilson says:
“The mere existence of ultramassive galaxies like XMM-2599 proves quite a challenge to numerical models. Even though such massive galaxies are incredibly rare at this epoch, the models do predict them. The predicted galaxies, however, are expected to be actively forming stars. What makes XMM-2599 so interesting, unusual, and surprising is that it is no longer forming stars, perhaps because it stopped getting fuel or its black hole began to turn on. Our results call for changes in how models turn off star formation in early galaxies.”
The astronomers don't know, however, what XMM-2599 will do in the future. Or, rather, the rest of the past. The weird thing about observing a galaxy like XMM-2599 is, due to its distance from Earth, they are looking at this galaxy as it was 11.7 billion years ago. Wilson says:
“We have caught XMM-2599 in its inactive phase. We do not know what it will turn into by the present day. We know it cannot lose mass. An interesting question is what happens around it. As time goes by, could it gravitationally attract nearby star-forming galaxies and become a bright city of galaxies?”
According to Michael Cooper, professor of astronomy at UC Irvine, and co-author of the new study describing XM-2599, this outcome is a strong possibility:
“Perhaps during the following 11.7 billion years of cosmic history, XMM-2599 will become the central member of one of the brightest and most massive clusters of galaxies in the local universe. Alternatively, it could continue to exist in isolation. Or we could have a scenario that lies between these two outcomes.”
Basically, it's a weird one. It's good to know that the universe can still get weird, though.