Observations of a star have found it orbiting an unexpectedly massive black hole. If the discovery pans out, it would change our understanding of how massive stars die.

Update (December 11, 2019): Since the publication of this research in Nature Astronomy, other astronomers have argued that the changes in velocity seen for the hydrogen-alpha emission line are not real. While the star still appears to orbit an unseen companion, which could still be massive enough to be a black hole, it wouldn’t necessarily be a heavyweight.

Star orbiting black hole
An artist's concept shows a hot, young star orbiting a black hole.
Jingchuan Yu / Beijing Planetarium

Astronomers have found a seemingly “impossible” black hole about 14,000 light-years away. Their observations, published in the November 28th Nature, suggest that the weird object weighs in at a staggering 68 times the mass of the Sun.

While much heftier black holes, dubbed supermassive, reside in the cores of most large galaxies, theories predict an upper limit of some 45 to 55 solar masses for a “stellar-mass” black hole that forms in the aftermath of a supernova explosion. According to Craig Wheeler (University of Texas, Austin), “This is clearly an interesting story, if verified.”

Stellar wobbles

So far, most stellar-mass black holes have been discovered via X-rays emitted by their hot accretion disks. But the new find didn’t show up in Chandra observations — it is truly invisible. Instead its existence was betrayed by the periodic wobble of a young, hot B-type subgiant star about eight times the mass of the Sun. This 11.5-magnitude star is in the westernmost part of Gemini. A survey carried out with the Chinese Large-sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) revealed the star’s motions toward and away from Earth as it orbited . . . something.

According to the team, led by Jifeng Liu (National Astronomical Observatories, Chinese Academy of Sciences), the star’s orbital period of 78.9 days and the observed velocity indicate that its companion has at least six times the Sun’s mass. Hence, it must be a black hole, because a star of that mass would be clearly visible. But that’s just its minimum mass — if we happen to be viewing the binary system from a steeper angle rather than exactly edge-on, the mass of the dark object could be much larger.

Star orbiting black hole
Another view of the star orbiting a monster of a stellar-mass black hole.
Jingchuan Yu / Beijing Planetarium

Here’s where the new discovery becomes intriguing: The spectroscopic data also show a broad emission line from ionized hydrogen, called hydrogen alpha, that does not move together with the other lines in the star’s spectrum. Instead, the line comes from something moving only one-eighth the speed of the star in its orbit.  What’s more, its motion is opposite the star’s, moving toward Earth as the star moves away and vice versa. These characteristics are just what you would expect for the star’s binary companion.

If the hydrogen-alpha emission originates in a large disk of hot gas orbiting the black hole, as the authors argue, then the observed velocity ratio translates directly into a mass ratio, indicating that the black hole is a whopping 68-solar mass monster. The corresponding distance between the black hole and the star orbiting it would be some 225 million kilometers, or 1.5 astronomical units (a.u.), comparable to the distance between Mars and the Sun.

Excitement vs. Skepticism

“About a week before the Nature publication, I received an email from the authors, around 2:45 a.m.,” says astrophysicist Selma de Mink (Center for Astrophysics, Harvard & Smithsonian). “I happened to be briefly awake, and habitually checked my phone. Bad idea. Couldn’t sleep anymore until the next morning.” The reason: 68-solar mass black holes shouldn’t exist.

“I’d love this to be true,” says de Mink, “since I really like mysterious puzzles about binary stars and black holes. But the hydrogen-alpha measurements are extremely difficult. I’m not yet convinced.”

Supernova expert Stan Woosley (University of California, Santa Cruz) is also skeptical of the high-mass claim. Extremely massive stars generally lose huge amounts of gas through stellar winds before they explode as supernova, especially when they are born in environments with relatively large amounts of elements heavier than hydrogen or helium (or metals, in astronomical parlance). That happens to be the case here: The accompanying star has some 20% more metals than the Sun.

“Of course, mass loss rates are notoriously uncertain,” Woosley admits. Still, he says no one expects a black hole 68 times as massive as the Sun to form in a region of near-solar metallicity. “This would be a qualitative change – hence interesting, but also requiring very compelling evidence. Thus, I remain skeptical, but I’m just a theorist. Observations rule.”

Team member Stephen Justham (University of Amsterdam) thinks the hydrogen-alpha measurements, on which everything hinges, are convincing enough to justify excitement. The LAMOST observations are supported by higher-precision data from the 10-meter Keck I and GranTeCan telescopes in Hawai’i and the Canary Islands, respectively. “If someone comes up with a better interpretation [for the motion of the hydrogen-alpha line], I’ll be very interested to hear,” he says.

Then again, Justham agrees that individual stars shouldn’t form such massive black holes, and he fully realizes “how shocking it would be” if the simple 68-solar mass black hole interpretation is true. For that reason, he suggested the idea that the dark mass in the binary system is not one massive black hole, but a close pair of them, each some 35 times the mass of the Sun.

Plot of black hole mergers
This plot shows the masses of black hole mergers detected by the LIGO and Virgo  gravitational wave detectors (blue), as well as the black holes detected via X-ray emission (purple). Also shown are neutron stars (yellow) and the LIGO-detected neutron star merger (orange). Click to see a larger version.
LIGO / VIrgo / Northwestern Univ. / Frank Elavsky

Indeed, LIGO and Virgo have detected gravitational waves from the mergers of black holes of up to 50 solar masses. So the new discovery could be a pre-merger binary black hole. Or maybe the pair has already merged, although that would be unlikely, given the young age of the system — the companion star is only 35 million years old.

There’s one additional problem. Parallax measurements by the European Space Agency’s Gaia spacecraft yield a distance of just 7,000 light-years to the star – twice as close as assumed based on the star’s spectrum and inferred true luminosity. However, the researchers note that the Gaia measurements are not very clean and are probably affected by the star’s binary wobble.

If Gaia’s distance measurement is true, however, then both the star and its invisible companion could be substantially less massive. At the same time, though, astronomers would have to assume that the star is in a rare out-of-equilibrium state in order to make it much less luminous than you would expect for a hot, young star of this type.

Follow Up and Future Finds

“I hope that the team will make their spectra publicly available,” says de Mink, “so that independent scientists can check the results.” She expects that it won’t be long before other telescopes will be trained on the system, carrying out new measurements. “Let’s see what happens.”

Woosley agrees there’s ample opportunity for more observations. “The system isn’t going anywhere,” he quips. Meanwhile, Justham thinks that future spectroscopic surveys will turn up many more quiescent black holes in binary systems. “Whatever the exact mass of this one,” he says, “it’s a taste of a future black hole population we’re only just starting to be able to discover.”

Comments


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redshiftbaron

November 28, 2019 at 9:18 am

Many mysteries in one system, fascinating!
By the way, a typo appears in the explanation of 'hydrogen alpha': it is an emission line from excited hydrogen, not ionized hydrogen.
Louis

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Rathgic

November 28, 2019 at 10:32 am

Black Holes are nothing but a very doubtful musing of Astronomers. They even said in the beginning if there are Black Holes then what (we have no doubt nor reason to doubt that gravity between masses IS INHERENT IN THE EXISTENCE OF THE MASS gravity) then gravity forces are suspended.

If they are not suspended and we have no reason to believe that gravity has any reason to be suspended for it is the essence of creating masses!!! then by the scientific method of determining the validity of scientific experiments, the supposed "theory" must be disregarded as having any truth or existence.

Simply repeating the original proposed "theory" over and over and artist drawing things with BLACK DOTS IN THEM MEAN NOTHING. And if fact what really is stupid, is that to the rest of us a BLACK DOT MEANS ONE OF TWO THINGS...... 1 SIMPLY THAT THERE IS NO LIGHT AVAILABLE TO ILLUMINATE WHAT MAY BE THERE OR 2 there is nothing there to exist and be seen.

They have had long enough to support their theory and simply building one huge supposition and "if" after another doesn't make the original "theory" of any value what so ever.
p

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AJames

November 29, 2019 at 9:20 pm

Mass is determined by orbital motion between the components. If star velocity of the star orbiting the black hole is known, then using simple Newtonian mechanics determines the mass of this invisible companion. (Is Newtonian mechanics regarding gravity therefore wrong?) Black holes are defined by relativity and the concept of spacetime, but they are still gravitational masses that affect their surroundings - like nearby stars. Gravity is not "suspended" when black holes are created, which is the wrongful premise of your assertions.

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Rathgic

November 28, 2019 at 11:05 am

And if you really want to know what theIe rational mistake is it is:

That inherent in the geometry of ARTIFICIAL ENLARGEMENT OF A VISUAL PICTURE OF OBJECTS HUGE LIGHT YEARS DISTANCE AWAY IS DONE BY INCREASING THE DISTANCE BETWEEN THOSE SMALLEST DOT SIZES THAT CAN REGISTER ON WHAT EVER IS REFLECTING THE IMAGE WE CAN SEE. BY THE SAME DISTANCE BETWEEN ALL OF THEM .

AND THAT PROCESS INHERENTLY BY THE REALITY GEOMETRY OF WHAT WE ARE ENLARGING IS EXAPANDING THE PICTURE IN .....ALL DIRECTIONS..... WHICH MEANS THERE IS A CENTER POINT FROM WHICH THE EXPANSION OCCURS. So let's take the two dots closest to the center ..... they expand outward for one smaller interval of the ultimate interval of the full expansion of the ultimate picture you show. And when they are expanded more than once in the distance between them of course there was nothing since they are going in opposite directions and they were side by side before enlargement.

And guess what? The center in which there are no dots has of course nothing. So in the ulltimate picture ARTIFICIALLY EXPANDED and not in real life THERE IS A BLACK SPOT THAT GET'S LARGER AND LARGER.

Of course, if you took a picture of a human, let's say and expanded it over light years of distance, and triedto do that in "real life" the human would die because the reality, only exist at the real life distance. Not the artificial distance of the ENLARGED PICTURE WHICH IS NOT REALITY. In real life ,, not an enlarged picture there is no space to put the characteristics of the astronomers alleged Black Hole that never existed in the first place. Only in the enlarged picture. And enlargement on earth of REAL THINGS ONLY MINUTE DISTANCES APART, OF COURSE, CAN BE DONE UP TO A POINT THAT THE OBJECT APPEARS TO REMAIN SOLID. Of course, that is not true in the picture. the dots were minutely separated further which is how the enlargment was created FOR THE NEW PICTURE..... NOT THE REALITY FROM WHICH THE PICTURE WAS MADE.
'
What I don't understand is why we should have to explain this kindergarten knowledge to PhD supposedly "smart" humans?????
s

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AJames

November 29, 2019 at 9:48 pm

Black holes are just not visible in any image, but are found by the influence on nearby material or nearby star(s). This behaviour outside the black hole deduces the properties of the black hole itself - like its mass, density, size, etc. (Sorry. Are you mixing up the expanding universe with black holes? There are far too many dead-wrong non-scientific ideas given above for anyone to correct your own misconceptions.)

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Rathgic

November 30, 2019 at 12:29 am

You are just going around in self supporting circles. "if the star velocity of the star orbiting the black hole. " You are assuming that a Black Hole Exist.
Black holes are just not visible in any image, but are found by the influence on nearby material or nearby star(s). This behaviour outside the black hole deduces the properties of the black hole itself.

what behavior?
We can't even see individual items in orbit of anything in the large blob of undefined "light" at the center of our own galaxy. .....at that huge distance and all asserted Black Holes are at that distance or beyond. Without identifying visually an independent entity of a free mass, you have nothing to determining the characteristics of it or that it even exist. Much less the characteristics of any anything other than there must be a lot of separate entities withing the blob of light we can see at the center of the milky way, for example where they assert A BLACK HOLE EXIST.
At that distance and beyond your aren't seeing anything but the enlargement of a blob of light that never resolves itself into anything specific entity of any kind that you can observe movement of at all.

and this is proof you don't know what you are talking about. It is a ignorant, unsubstantiated claim that what I said was wrong and blame me from two many dead wrong non-scientific ideas. But never give an example of anything I said was wrong. Astronomy "research" for the most part lost any semblance of a scientific method of research long ago.

You say: Black holes are just not visible in any image, but are found by the influence on nearby material . You are assuming but do not describe any specific entity that exist as an independent motion entity that you can "see" to determine something about it .....much less WHAT THE CHARACTERISTICS OF IT ARE IE; BEING IN ORBIT OR ANYTHING ELSE ABOUT IT. the characteristics of it ....for getting for a moment , always at distances as great as the center of our galaxy or greater. that would qualify as having identified as "nearby material".

In fact one of the characteristics you give your supposed entity from which you can determine some "influence" exist is a blob of light that is absurdly large single entity for which there is absolutely no reason to assume that blob is a single entity any more that less enlarged blobs, at the center of our galaxy at the maximum artificial enlargement years ago possible did not represent any one entity from which an "influence characteristics" on anything else around it it could be determine. Certainly a large blob of light that obviously contains many smaller entities can not determine anything about an individual entity within it like that it is orbiting around any single entity much less "the characteristics of the orbit" much less also that one thing in that blob is "influencing " another in a specific way causing anything. Your statement "This behavior outside the Black Hole" deduces the properties of the black hole" Does not refer to any specific entity much less its "behavior". But just like the absurdity of saying Black Holes exist..... they now assert all sorts of supposed single entities that are absurd light years across.

The problem is not me the problem is YOUR DEAD- UNSUPPORTED ABSURD IDEAS THAT IN NO WAY QUALIFY AS "SCIENTIFIC IDEAS" And in fact this type of absurd assertion of reality is duplicated by the other end of the "size spectrum" with supposed entities much smaller than the sub parts of atoms to which they assert as correct reality their description of the characteristics of these also "unseen" entities.

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AJames

November 30, 2019 at 7:44 pm

This article says : "...the star’s orbital period of 78.9 days and the observed velocity indicate that its companion has at least six times the Sun’s mass. Hence, it must be a black hole, because a star of that mass would be clearly visible."
If it were that : "You are just going around in self supporting circles. “if the star velocity of the star orbiting the black hole. ” You are assuming that a Black Hole Exist." But if the unseen gravitational source weighs 68 solar masses, deduced by the high orbital velocity of the companion, then what is it? (If it were a true star, it would be highly luminous. We don't see that.) Evidence strongly meets the very definition of a black hole.
What is YOUR ACTUAL EVIDENCE that it denies it is a black hole (other than mere hearsay)?

Note : As for "But just like the absurdity of saying Black Holes exist….. they now assert all sorts of supposed single entities that are absurd light years across." Who has ever been said black holes can ever reach this size? The supermassive black hole (SMBH) in our Milky Way is about 12 million kilometres across defined by calculating its Schwarzschild radius via r=2GM/c^2, where its mass is 4.1 million times the Sun. Q. What is an object called that has 4.1 million solar masses and is 12 million km across?

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qraal

November 29, 2019 at 4:06 pm

Hi S&T
The same day that the discovery paper hit the arXiv preprint server a preprint explaining how such black holes can form appeared...
https://arxiv.org/abs/1911.12357
Thus the "mystery" isn't that mysterious - although it is still cool 🙂

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qraal

November 29, 2019 at 4:09 pm

The discovery preprint is here... https://arxiv.org/abs/1911.11989

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Jim Slater

November 29, 2019 at 5:37 pm

Is LB-1 is located at 188.23526° (Galactic longitude), +02.05089° (Galactic latitude) in the constellation Gemini at an estimated 3,800 light years from Earth. Is this AWAY from the Galactic Center relative to Earth, or TOWARD the Galactic Center relative to earth? What is its estimated distance from the Galactic Center?

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GH Martin

November 30, 2019 at 8:55 pm

Anything seen in the direction of Gemini is AWAY from the galactic center. 180º galactic longitude, 0º galactic latitude is directly opposite the center of the Milky Way galaxy (from Earth).

Easy way to tell, just using your eyes -- the galactic center is in Sagittarius, and Gemini is just rising in the northeast as Sagittarius is setting in the southwest.

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GH Martin

November 29, 2019 at 9:58 pm

Could the alleged 68-solar mass black hole be the result of a merger? We know now that this happens (thanks, LIGO)

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Rod

November 30, 2019 at 8:50 am

FYI. Some of the comments here remind me of flat earth community teaching about astronomy and gravity (there is no such thing as gravity and Einstein GR is myth). The Nature report in the Abstract states "...Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star–black-hole binaries5,6. When the black hole is not accreting gas, it can be found through radial-velocity measurements of the motion of the companion star. Here we report radial-velocity measurements taken over two years of the Galactic B-type star, LB-1. We find that the motion of the B star and an accompanying Hα emission line require the presence of a dark companion with a mass of 68...solar masses, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system..." This interpretation and theory of the observations is based upon Einstein General Relativity and the radial velocity method of detection is used successfully in exoplanet studies too. The site I use (http://exoplanet.eu/) shows 4133 exoplanets confirmed since 27-Nov-19 (now 4135 as of today), 863 detected by radial velocity method. showing 863 exoplanets confirmed by the radial velocity method is similar to showing the B-type star is real and orbiting according to gravity - pointing to a large, black hole mass near 68 solar. With gravity, we can measure the size and mass of the Sun and the Earth as well as detect other objects orbiting larger bodies too (e.g. the Galilean moons orbiting Jupiter 🙂

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