Thread by @planet4589

I thought I'd give my own spin on Abbie's black hole tweet (although you should read her own discussion of it and follow her at @abigailStev ) ....

@abigailStev What is 4U 1543-47? It's a 'high mass X-ray
binary', a binary star with an A-type main sequence star called IL Lupi, about twice as massive as the Sun, tightly orbiting a black hole 9 times the mass of the Sun.

@abigailStev The two objects are so close to each other that matter from the
A star is being torn off and collects in a disk
around the black hole, slowly trickling in.

@abigailStev Sometimes a big blob
of starstuff falls towards the black hole, releasing a
lot of energy in the form of X-ray light before it disappears
forever down the event horizon.

@abigailStev 4U 1543-47 is 25,000 light years away, in a direction in the sky between Eta Normae and Nu-1 Lupi, on the border of the southern constellations Lupus and Norma.
(constell diag from Sky and Tel)

@abigailStev 4U 1543-47 was first observed as an X-ray outburst in July 1971 by the US Air Force's Vela satellite, scanning for nuclear explosions - which
this was, just not the sort they were looking for! The Air Force didn't publish the information at the time.

@abigailStev It was the American Science and Engineering
team in Cambridge, MA (who later became the Center for Astrophysics team
that operates Chandra) who officially discovered the object using the Uhuru satellite, reporting it in IAU Circular 2355 in 1971.

@abigailStev Terry Matilsky and his colleagues at AS&E wrote up the detailed paper of the discovery in 1972 ui.adsabs.harvard.edu/abs/1972ApJ...…

@abigailStev What does the weird name mean? The 1543-47 gives the object's location
in the sky: 15 hours 43 minutes of right ascension (the astronomer's
version of longitude) and minus 47 degrees declination (astronomer's latitude).

@abigailStev (Technical point: this is its location in the old B1950 system; its
location in the modern ICRS system is 1547-47).

@abigailStev The 'U' flags it as
being a discovery by Uhuru, the first satellite to map the sky in X-rays. '4U' because it took the team 4 tries to get a really good catalog of the Uhuru data with a minimum of mistakes in it, you should throw away your 2U and 3U catalogs, they're not as good

@abigailStev These 'X-ray transients' were originally called 'X-ray novae' - they are always shining in X-rays, but usually quite faintly.

@abigailStev Once in a while they gulp down a bit lump and get really bright for a while. This is what is blinding the ISS's NICER telescope and interrupting Abbie's vacation. Have fun with the data, Abbie!