Next Week’s Night Sky:
When the moon reaches its third quarter phase at 17:37 GMT (or 12:37 p.m. EST) on Thursday, Feb. 4, it will rise in the middle of the night, and then remain visible in the southern sky all morning. At this phase the moon is illuminated on its western side, towards the pre-dawn Sun. Third quarter moons are positioned ahead of the Earth in our trip around the Sun. About 3½ hours later, Earth will occupy that same location in space. The week of moonless evening skies that follow the third quarter will be ideal for observing deep sky targets.
Missing supermassive black hole
Astronomers have been searching for a 10 billion solar-mass black hole at the heart of a truly massive galaxy for the past decade.
They still haven’t found it.
The galaxy in question, A2261-BCG, is the most massive member of the remote Abell 2261 galaxy cluster some 2.7 billion light years away in the constellation Hercules. It is gargantuan by almost any standard, spanning about 10 times the width of the Milky Way. Its core alone measures about 10,000 light years across, the largest yet seen.
All large galaxies are thought to harbour a supermassive black hole. The mass of the black hole generally scales with the mass of the host galaxy, meaning A2261-BCG should be home to a black hole with 3 billion to 10 billion times the mass of the Sun.
Despite careful searches by the Hubble Space Telescope and the Chandra X-ray Observatory, the presumed black hole is nowhere to be found.
So where could it be?
Black holes, by definition, cannot be directly observed because their enormous gravity prevents even light from escaping. But as they suck in surrounding dust and debris, even stars, the material is heated to extreme temperatures, releasing torrents of detectable radiation. No such radiation has been seen from the core of A2261-BCG.
The galaxy’s central black hole could be in a quiescent stage, having devoured nearby debris and not pulling enough in to generate detectable levels of radiation. Four clumps of stars have been identified where the black hole could be lurking.
More intriguing, it’s also possible the galaxy is the result of two galaxies colliding, leading to the eventual merger of two supermassive black holes.
Such a merger would have generated powerful gravitational waves in the fabric of space. If the gravitational distortions were not symmetric, the resulting mega black hole could have been ejected from the galaxy in the opposite direction.
The James Webb Space Telescope, scheduled for launch in October, may be able to spot the elusive black hole near the centre of the galaxy or in one of four star clumps identified to date. If the JWST can’t find any signs of the black hole, then the recoil scenario may be the best explanation.
Sextuple star system
Astronomers studying data from NASA’s Transiting Exoplanet Survey Satellite, or TESS, have found a remarkable sextuple star system featuring three gravitationally bound eclipsing binaries.
The system, known as TYC 7037-89-1, is located about 1,900 light years from Earth in the constellation Eridanus. It is the first known example of six stars making up a trio of eclipsing binaries, known as A, B and C.
The primary stars in all three binaries undergo periodic eclipses, passing in front of each other as viewed by TESS. The changing light curves show all three primary stars are slightly more massive than the sun, but about as hot. The secondary stars are roughly half the size the Sun.
The two stars making up the A binary orbit each other every 1.3 days while the stars in binary C orbit each other every 1.6 days. The A and C binary systems, in turn, orbit each other every four years. The two stars in the B system orbit each other every 8.2 days, but they take about 2,000 years two complete an orbit around the sextuple system’s center of gravity.
Multiply-eclipsing multiple systems such as TYC 7037-89-1 enable simultaneous, precise measurements on the stellar sizes, temperatures, and potentially masses, of pairs of stars that share common history. In turn, this provides better understanding of stellar formation and evolution in dynamically-rich environments.
Do you have any cool astronomy research news from this week? Share it in the comments below!