Multiple black holes at centre of our galaxy

There is not just one black hole at the centre of the Milky Way galaxy (as i had thought). Scientists have discovered about a dozen smaller black holes, and say their could be tens of thousands.

Black Hole Sun

Smithsonian: The Center of the Milky Way May Be Chock-Full of Black Holes

Black holes emit no visible light or radiation, making them extremely difficult to directly observe using our current technology. But scientists can study how they interact with bodies nearby. For the latest find, researchers picked up the signal from a star orbiting the black hole, which causes the system to emit X-ray radiation.

For the latest study, a team headed by the Columbia University astrophysics lab picked through 12 years of data collected by NASA’s Chandra X-Ray Observatory on a search for the telltale radiation within 13 light-years of the galactic center. As Phil Charles, an astrophysicist at the University of Southampton who was not involved in the study, explains for The Conversation, the team found about 100 X-ray sources in that search area, including 26 signals within three light-years of Sagitarrius A*.

“It’s the confirmation of several theories that predicted this ought to be the case,” says Chuck Hailey, a Columbia astrophysicist and first author of the study, reports ​Gizmodo’s Ryan F. Mandelbaum. “But it’s strange to have had this many and not really see them.”

According to a press release, the researchers estimate that based on the spatial distribution of the black holes they found, there are probably 300 to 500 black hole binaries in the immediate region around Sagitarius A* and about 10,000 isolated black holes not orbited by stars.

As Sarah Gibbens at National Geographic reports, those estimates are based on the theory that about 1 in 20 black holes will attract a low-mass star. Even if that calculation is slightly off, Gibbens reports, there are still likely way more black holes than the 60 or so scientists have yet detected.

While 10,000 black holes sounds like a lot, it’s a tiny fraction of the total number of black holes scientists estimate the Milky Way contains. Based on current calculations, there are 100 million stellar-mass black holes in our galaxy alone. And here’s something crazy to consider: One new black hole likely forms somewhere in the universe every single second.

NPR: Center Of The Milky Way Has Thousands Of Black Holes, Study Shows

For decades, scientists have thought that black holes should sink to the center of galaxies and accumulate there, says Chuck Hailey, an astrophysicist at Columbia University. But scientists had no proof that these exotic objects had actually gathered together in the center of the Milky Way.

He and his colleagues recently went hunting for black holes, using observations of the galactic center made by a NASA telescope called the Chandra X-ray Observatory.

Isolated black holes are almost impossible to detect, but black holes that have a companion — an orbiting star — interact with that star in ways that allow the pair to be spotted by telltale X-ray emissions. The team searched for those signals in a region stretching about three light-years out from our galaxy’s central supermassive black hole.

“So we’re looking at the very, very, very center of our galaxy. It’s a place that’s filled with a huge amount of gas and dust, and it’s jammed with a huge number of stars,” Hailey says.

What they found there: a dozen black holes paired up with stars, according to a report in the journal Nature.

Finding so many in such a small region is significant, because until now scientists have found evidence of only about five dozen black holes throughout the entire galaxy, says Hailey, who points out that our galaxy is 100,000 light-years across. (For reference, one light-year is just under 5.88 trillion miles.)

Looking at the centre of the Milky Way is tricky from our solar system as it’s necessary to look through a huge number of stars. We are about half way between the centre and the rim, both about 25,000 light years distant, as shown here:

Milky Way and Our Location

It takes our solar system about 250 million years to orbit the galaxy.

Of course scientists and artists can only imagine what it actually looks like, there is no way of viewing it, but we can guess what it is like from scientific observations and how other spiral galaxies look (but given the diversity of stuff in space there’s no guarantee the Milky Way is similar to other galaxies we can see from here.

There is a very rough estimate of 250 billion stars in the Milky Way, ± 150 billion so a huge margin of error.

Hubble telescope observations have revealed an estimated 100 million galaxies in the universe but with more detailed observations it is thought this could double.

So there is going to also be a huge number of black holes, the things that are impossible to see because light can’t escape them but scientists can somehow detect.

Around what?

NASA discovered that there was a satellite rock orbiting the asteroid that passed close by Earth earlier this week.

NASA has discovered a tiny moon 70 meters (230 feet) in diameter circling the asteroid that passed very close to Earth earlier this week, a situation that occurs in just 16 percent of the cases of known asteroids.

The tiny moon is orbiting the asteroid, which itself is only 325 meters (about 1,060 feet) in diameter.

If this asteroid went close enough to the moon it could get trapped into orbit.

Then there would be a moon around a moon around the Moon.

Around Earth. Around the Sun. Around the Milky Way. Around the Universe.

Around what?