Killer black hole mapped from its own feeding
Friday, November 25, 2016, 1:54 PM - Astronomers watch as a slumbering giant devours a star, and NASA discovers that an invisible 'electric wind' stripped away Venus' water. It's #BlackHoleFriday!
'Killer' black hole mapped from its own feeding
Mapping a supermassive black hole is extremely difficult, primarily because, as a seemingly bottomless pit in spacetime, there's nothing to actually see there, unless there happens to be a bright disk of matter - an accretion disk - feeding the black hole. Even so, the black hole needs to be quite active to get our attention and we usually need to catch it just at the right time to actually get enough information to tell us anything.
So, based on that, it's easy to imagine just how hard it would be to map a dormant black hole - one that long ago consumed any matter around it, thus has no accretion disk.
Well, as NASA astronomer Erin Kara discusses in the video above, a chance encounter, 3.8 billion years ago, can afford us some measure of luck when it comes to detecting these slumbering giants.
"While we don't yet understand what causes X-ray flares near the black hole, we know that when one occurs we can detect its echo a couple of minutes later, once the light has reached and illuminated parts of the flow," Kara explained in a NASA statement. "This technique, called X-ray reverberation mapping, has been previously used to explore stable disks around black holes, but this is the first time we've applied it to a newly formed disk produced by a tidal disruption."
'Electric wind' dries out Venus
For some years now, scientists have been puzzling over how dry it is on Earth's sister planet, Venus.
From the looks of surface features on Venus, the planet definitely had liquid water oceans at some point in the distant past, when our Sun was cooler. Sure, it's sweltering hot there now (around 465oC on average), but that would just turn the water to steam and split some of it into its components - hydrogen and oxygen. The heat, alone, shouldn't result in the loss of all the water on the planet, though.
It turns out that it's not the heat that's making Venus so dry. It's the planet's "electric wind." Here's NASA researcher Glyn Collinson, the lead author of a new paper that describes the action of this "wind," to talk about it:
So, what it comes down to is Venus' extreme electric field - which is over five times stronger than the electric field of Earth - accelerating the charged oxygen ions to such speeds that they can achieve escape velocity and leave Venus' atmosphere.
"If you were unfortunate enough to be an oxygen ion in the upper atmosphere of Venus then you have won a terrible, terrible lottery," Collinson said in a NASA press release, "You and all your ion friends will be dragged off kicking and screaming into space by an invisible hand, and nothing can save you."