-Daniel aka Obsidian
Black holes are very dense, massive objects in space that have an immensely powerful gravitational field that traps anything and everything that comes too close, including light. But on occasion they'll spit out material as well as suck it in. On June 15, one of NASA's satellites picked up a torrent of x-rays all coming from a single source: the black hole.
"Relative to the lifetime of space observatories, these black hole eruptions are quite rare," said Neil Gehrels, the principal investigator for Swift, the NASA satellite that first identified the eruption in a NASA press release. "So when we see one of them flare up, we try to throw everything we have at it, monitoring across the spectrum, from radio waves to gamma rays."
A deadly companionThis black hole is just one half of a two-body system called V404 Cygni. Its partner is a star slightly smaller than our sun, and it's been nourishing the black hole for at least 77 years. The x-rays that astronomers observed on June 15 were the heated guts from the companion star that had spiraled into the mouth of the black hole.
When black holes in binary systems, like V404 Cygni, feed, they do so by gravitationally attracting a single thread of gas from the star. The black hole is 12 times more massive than its companion and therefore has a much stronger gravitational grip which slowly pulls gas from the star as the star orbits around it, like in the animation below:
But there isn't always a steady stream of gas falling into the black hole, which is why it takes such long naps in between feedings. That disc has two regions: and inner, hot region, and an outer cool region. You need a lot of gas to provide enough pressure and push to cross this barrier, which takes time to generate. Once the black hole has consumed all of the gas in the inner region, which it does in a few days, it has to wait for more. But scientists don't understand the details of how much gas is necessary or exactly how long it takes to build up.
That's why this event is so exciting because it gives astronomers a chance to better understand the mechanism that's driving these eruptions.
A once-in-a-professional-lifetime opportunity
However, when astronomers first saw the outbursts more than 77 years ago, in 1938, they didn't have half of the instruments that are around today. The black hole erupted again in 1956, and then again in 1989.
While the eruption of 1989 was studied with a handful of instruments, the outburst wasn't studied in half the detail compared to this year's event. Outbursts like this usually only last for a few weeks to months, so astronomers have culminated a total of nine instruments in space and on the ground to study the black hole in all wavelengths, from very low energy like radio waves to the most energetic like gamma rays, before time runs out.
Some of the instruments they're using include the Chandra X-ray Observatory, the European Space Agency's INTEGRAL satellite, Japan's MAXI, and the 10.4-meter Gran Telescope Canarias operated by Spain in the Canary Islands.
"It is definitely a 'once in a professional lifetime' opportunity," said Erik Kuulkers, the INTEGRAL project scientist in the NASA press release.