How much of the universe is black holes?

Supermassive black holes are enormously dense objects buried at the hearts of galaxies. 

Credit: NASA/JPL-Caltech

We all fear black holes, but how many of them are there out there, really?

Between the stellar mass black holes and the supermassive ones, just how much of our Universe is black holes?

There are two kinds of black holes in the Universe that we know of: There's stellar mass black holes, formed from massive stars, and a supermassive black holes which lives at the hearts of galaxies.

About 1 in a 1000 stars have enough mass to become a black hole when they die. Our Milky Way has 100 billion stars, this means it could have up to 100 million stellar mass black holes.

As there are hundreds of billions of galaxies in the observable Universe, there are lots, lots more out there.

In fact, the math suggests there's a new black hole forming every second or so. So just to recap, the entire Universe is about 1/1000th "regular flavor" stellar mass black holes.

Supermassive black holes are a slightly different story. Our central galactic black hole is about 26,000 light years away from us.

Formally, it's called Sagittarius A-star, but for our purposes I'm going to call it Kevin. Just so you know they don't throw that term "supermassive" around for no reason, Kevin contains 4.1 million times the mass of the Sun.

Kevin is gigantic and horrible. We can only imagine what it's like to be in the region of space near Kevin. What percentage of the galaxy do you think Kevin makes up, mass wise?



Kevin, whilst absolutely super-massive, is a tiny, tiny 1/10,000 of a percent of the Milky Way galaxy's mass.

So, to be precise, if we add Kevin's mass to the mass of all the stellar mass black holes aka. "mini-Kevins", we get a very minor 11/10000s of a %.

As it turns out this ratio holds up on a Universal scale and is approximately the same for all the mass in the Universe. So, 11 ten thousandths of a percent is the answer to the question. As far as we know.

Unless… dark matter is black holes. Dark matter accounts for more than ¾ of the mass of the Universe. It doesn't absorb light or interact with matter in any way. We're only aware of its presence through its gravitational influence.

As it turns out, Astronomers think that one explanation for dark matter might be primordial black holes.

These microscopic black holes would have the mass of an asteroid or more and could only form in the high pressure, high temperature conditions after the Big Bang.

Experiments to search for primordial black holes have yet to turn up any evidence, and most scientists don't think they're a viable explanation. But if they were, then the Universe is almost entirely composed of the physics inspired nightmare that are black holes.

Chandra Sagittarius A*: Black holes at centre of galaxies are wormholes

Credit: X-ray: NASA /UMass /D.Wang et al., IR: NASA/STScI

Zilong Li and Cosimo Bambi with Fudan University in Shanghai have come up with a very novel idea, those black holes that are believed to exist at the center of a lot of galaxies, may instead by wormholes.

They've written a paper, uploaded to the preprint server arXiv, describing their idea and how what they've imagined could be proved right (or wrong) by a new instrument soon to be added to an observatory in Chile.

Sagittarius A*: NASA's Chandra Finds Milky Way's Black Hole may be Grazing on Asteroids

Back in 1974, space scientists discovered Sagittarius A* (SgrA ∗), a bright source of radio waves emanating from what appeared to be near the center of the Milky Way galaxy.

Subsequent study of the object led scientists to believe that it was (and is) a black hole, the behaviour of stars nearby, for example, suggested it was something massive and extremely dense.

What we're able to see when we look at SgrA ∗ are plasma gasses near the event horizon, not the object itself as light cannot escape.

That should be true for wormholes too, of course, which have also been theorized to exist by the Theory of General Relativity. Einstein even noted the possibility of their existence.

GRAVITY overview. The beam combiner instrument (bottom right) is located in the VLTI laboratory. 

The infrared wavefront-sensors (bottom left) are mounted to each of the four UTs. 

The laser metrology is launched from the beam-combiner and is detected at each UT/AT (top middle).

Unfortunately, no one has ever come close to proving the existence of wormholes, which are believed to be channels between different parts of the universe, or even between two universes in multi-universe theories.

In their paper, Li and Bambi suggest that there is compelling evidence suggesting that many of the objects we believe to be black holes at the center of galaxies, may in fact be wormholes.

Plasma gases orbiting a black hole versus a wormhole should look different to us, the pair suggest, because wormholes should be a lot smaller.

Plus, the presence of wormholes would help explain how it is that even new galaxies have what are now believed to be black holes, such large black holes would presumably take a long time to become so large, so how can they exist in a new galaxy?

They can't Li and Bambi conclude, instead those objects are actually wormholes, which theory suggests could spring up in an instant, and would have, following the Big Bang.

Making the two's speculation more exciting is the soon to be installed piece of equipment known as GRAVITY, it will be added to the European Space Observatory (ESO) in Chile, giving researchers there an unprecedented view of SgrA ∗ (and other black holes).

In just a couple of years, it should be possible to prove whether Li and Bambi's idea is correct or not, the photon capture sphere of the wormhole should be much smaller than that for a black hole, they note, if that's the case with SgrA ∗, space scientists will have to do some serious rethinking of wormholes and how they might fit in to current theories describing the universe.

More information: Distinguishing black holes and wormholes with orbiting hot spots, arXiv:1405.1883

Chandra confirm evidence of jet in Milky Way's black hole

Composite image of Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way. 

Credit: X-ray: NASA /CXC /UCLA /Z. Li et al; Radio: NRAO /VLA

Astronomers have long sought strong evidence that Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, is producing a jet of high-energy particles. 

Finally they have found it, in new results from NASA's Chandra X-ray Observatory and the National Science Foundation's Very Large Array (VLA) radio telescope.

Previous studies, using a variety of telescopes, suggested there was a jet, but these reports—including the orientation of the suspected jets—often contradicted each other and were not considered definitive.

"For decades astronomers have looked for a jet associated with the Milky Way's black hole. Our new observations make the strongest case yet for such a jet," said Zhiyuan Li of Nanjing University in China, lead author of a study appearing in an upcoming edition of the Astrophysical Journal and available online now.

Jets of high-energy particles are found throughout the universe, on large and small scales. They are produced by young stars and by black holes a thousand times larger than the Milky Way's black hole.

They play important roles in transporting energy away from the central object and, on a galactic scale, in regulating the rate of formation of new stars.

"We were very eager to find a jet from Sgr A* because it tells us the direction of the black hole's spin axis.

This gives us important clues about the growth history of the black hole," said Mark Morris of the University of California at Los Angeles, a co-author of the study.

The study shows the spin axis of Sgr A* is pointing in one direction, parallel to the rotation axis of the Milky Way, which indicates to astronomers that gas and dust have migrated steadily into Sgr A* over the past 10 billion years.

If the Milky Way had collided with large galaxies in the recent past and their central black holes had merged with Sgr A*, the jet could point in any direction.

The jet appears to be running into gas near Sgr A*, producing X-rays detected by Chandra and radio emission observed by the VLA.

The two key pieces of evidence for the jet are a straight line of X-ray emitting gas that points toward Sgr A* and a shock front—similar to a sonic boom—seen in radio data, where the jet appears to be striking the gas.

Additionally, the energy signature, or spectrum, in X-rays of Sgr A* resembles that of jets coming from supermassive black holes in other galaxies.

Scientists think jets are produced when some material falling toward the black hole is redirected outward. Since Sgr A* is presently known to be consuming very little material, it is not surprising that the jet appears weak.

A jet in the opposite direction is not seen, possibly because of gas or dust blocking the line of sight from Earth or a lack of material to fuel the jet.

The region around Sgr A* is faint, which means the black hole has been quiet in the past few hundred years.

However, a separate Chandra study announced last month shows that it was at least a million times brighter before then.

"We know this giant black hole has been much more active at consuming material in the past. When it stirs again, the jet may brighten dramatically," said co-author Frederick K. Baganoff of the Massachusetts Institute of Technology in Cambridge, Mass.

More information: "Evidence for a Parsec-scale Jet from the Galactic Center Black Hole: Interaction with Local Gas," Zhiyuan Li, Mark R. Morris, and Frederick K. Baganoff. xxx.lanl.gov/abs/1310.0146