NOTE ADDED: FALSE ALARM! DISREGARD! HERE’S SWIFT’S DETAILED EXPLANATION AS TO WHY! with my own brief summary below.
Comparable in size to the Milky Way, our host galaxy, the Andromeda galaxy is the most distant object easily visible (in dark skies) to the naked eye; it lies 2.5 million light-years away.
About 2.5 million years ago, something in this distant star city went “boom”. And in doing so it flashed, brightly, in high-energy photons — particles of light (or, more precisely, particles of electromagnetic radiation, of which visible light is just an example) — photons that carry many thousands of times more energy than do the photons that our eyes are designed to see.
The Andromeda Galaxy (photo from Creative Commons), which contains perhaps 100 billion stars or more. Something in here exploded a while back, and we just found out about it.
Some of these photons, after traveling for millions of years across space, arrived at Earth this afternoon. They showed up in the Swift satellite’s telescopes, which are designed precisely to notice these things. And Swift’s telescopes identified these photons as arriving from a location somewhere within Andromeda… within a globular cluster of stars, a tightly-knit neighborhood within the city that is Andromeda. NOTE ADDED: Actually, a combination of low-probability events caused
- a false alarm, of a sort that’s rare but not unexpected: a known object in Andromeda that emits X-rays appeared to brighten, as a result of electronic noise in Swift’s instruments (such noise is always present, in all scientific instruments, and it is normal to occasionally get a strong burst of it)
- followed (
due perhaps to a poorly-timed computer problem at Swift’s data center, which slowed the arrival of more complete information the Swift people know why but haven’t explained it in detail) by a delay in identifying this apparent brightening as a false alarm;
all of which is explained here. The apparent brightening, which was rather mild, would in fact have been completely disregarded if it hadn’t occurred in Andromeda; for relatively nearby objects like Andromeda, the Swift team sets a low threshold for false alarms, because something real would be so amazingly important and exciting that we can’t afford to miss it.
What caused this
colossal explosion, perhaps the nearest of its type ever observed by modern astronomers? That is the burning question that astronomers, and their friends in gravitational physics and particle physics, are aching to know. It is likely that by tomorrow morning, and certainly within the next couple of days, we’ll know much more… perhaps we’ll even learn something of great importance. NOTE ADDED: And indeed, we know.
For the moment, though, there’s lots of guessing,
most all of which will turned out to be wrong. (Maybe, some are speculating, this is a gamma-ray burst, perhaps caused by a merger of two neutron stars, with consequent bursts of neutrinos and gravitational waves that we might detect; but right now there’s no evidence for this, so don’t get your hopes up.) You can read many breathless articles by following the Twitter hashtag #GRBm31. Admittedly you might be better off without it. NOTE ADDED: Yep.
But do stay tuned as the facts emerge. The opportunity to observe such a nearby explosion is rare. So this is certainly going to be interesting… and maybe, if we’re very lucky, it will be more than merely interesting…
NOTE ADDED: Actually, we were very unlucky, and it was completely uninteresting —except as an illustration that it can be very difficult, in the heat of a moment when data is sparse, to distinguish between something scientifically fascinating and a weird fluke. Scientists do expect these things to happen sometimes. Fortunately, science is self-correcting. Even if Swift’s team hadn’t identified this signal as a fluke in their data, other telescopes would have been unable to find the object they’d identified, and doubts would quickly have emerged as a result. If something’s real, everyone will see it.
The lesson, in my view, is that when new scientific results are announced, be patient. Give the experts a little time to check things, and don’t do science the way Twitter does.
And finally: if you are inclined to criticize the Swift team, you’re making a big mistake. On the contrary, they did exactly what they were supposed to do, as quickly as they could. Gamma-ray bursts [GRBs] are extremely rare and extremely valuable and extremely brief; Swift’s job is to let the scientific community know, as quickly as possible, that one may have been seen, so that others may look at it. Inevitably, someone with such a job will occasionally give a false alarm. Swift has discovered so many GRB’s, and made so many direct and indirect contributions to our knowledge about them and about other objects in the sky, that scientists, while disappointed that this was a false alarm, will certainly not view Swift as irresponsible.
A week ago, regarding BICEP2′s results coming into question, Seth Zenz wrote a nice, short article on Why, in Science, it’s OK to be Wrong. I recommend it.