Astronomers Complete the Puzzle of Black Hole Description


Light may not be able to escape a black hole, but now enough information has escaped one black hole’s clutches that astronomers have, for the first time, been able to provide a complete description of it. A team of astronomers from the Harvard-Smithsonian Center for Astrophysics (CfA) and San Diego State University have made the most accurate measurements ever of X-ray binary system Cygnus X-1, allowing them to unravel the longstanding mysteries of its black hole and to retrace its history since its birth around six million years ago.

Cygnus X-1, which consists of a black hole that is drawing material from its massive blue companion star, was found to be emitting powerful X-rays nearly half a century ago. Since its discovery in 1964, this galactic X-ray source has been intensely scrutinized with astronomers attempting to gain information about its mass and spin. But without an accurate measurement of its distance from the Earth, which has been estimated to be between 5,800 and 7,800 light-years, we could only imagine what secrets Cygnus X-1 was harboring.

Astronomer Mark Reid of CfA led his team to garner the most accurate measurement of the distance to Cygnus X-1 with the help of the National Science Foundation’s Very Long Baseline Array (VLBA), a continent-wide radio-telescope system. The team locked down a direct trigonometric measurement of 6,070 light-years.

“Because no other information can escape a black hole, knowing its mass, spin and electrical charge gives a complete description of it,” says Reid who is a co-author of three papers on Cygnus X-1, published in the Astrophysical Journal Letters (available here, here, and here). “The charge of this black hole is nearly zero, so measuring its mass and spin make our description complete.”

Using their new precise distance measurement along with the Chandra X-ray Observatory, the Rossi X-ray Timing Explorer, the Advanced Satellite for Cosmology and Astrophysics and visible-light observations made over more than two decades, the team pieced together the “No Hair” theorem – the complete description that Reid speaks of – by revealing a hefty mass of nearly 15 solar masses and a turbo spin speed of 800 revolutions per second. “We now know that Cygnus X-1 is one of the most massive stellar black holes in the Milky Way,” says Jerry Orosz of San Diego State University, also an author of the paper with Reid and Lijun Gou of the CfA. “It’s spinning as fast as any black hole we’ve ever seen.”

As an added bonus, observations using the VLBA back in 2009 and 2010 had also measured Cygnus X-1’s movement through the galaxy leading scientists to the conclusion that it is much too slow to have been produced by the explosion of a supernova and without evidence of a large “kick” at birth, astronomers believe that it may have resulted from the dark collapse of a progenitor star with a mass greater than about 100 times the mass of the Sun that got lost in a vigorous stellar wind. “There are suggestions that this black hole could have formed without a supernova explosion and our results support those suggestions,” says Reid.

It seems that with these measurements, Professor Stephen Hawking has well and truly had to eat his own words after placing a bet with fellow astrophysicist Kip Thorne, a professor of theoretical physics at the California Institute of Technology, that Cygnus X-1 did not contain a black hole.

“For forty years, Cygnus X-1 has been the iconic example of a black hole. However, despite Hawking’s concession, I have never been completely convinced that it really does contain a black hole – until now,” says Thorne. “The data and modeling in these three papers at last provide a completely definitive description of this binary system.”

Sources: CfA

16 Replies to “Astronomers Complete the Puzzle of Black Hole Description”

  1. I think this needs a link…”dark collapse of a progenitor star”. What’s a dark collapse? Did it just burn out and then implode? And are all post-nova star remnants speeding along somewhere? Couldn’t their explosion let them remain pretty much centred?

    1. Dark would mean “not supernova” by context, is how I read it. I know, that is like saying a fire is dark because it can be compared with daylight.

      I don’t understand the remaining questions, what nova are we talking about if Cygnus X-1 is a “mere” collapse combined with mass losses in stellar winds? Wolf–Rayet stars creates a nebula, not a nova, it seems to me.

      1. Basically, he asks if every SN gives a kick. Maybe, some symmetric SN would keep it at the same place. And when they get kicked where do they go. 🙂

      2. if they are kicked (and neutron stars) and they had a close companion who received a significant amount of mass prior, they might end up as BeX-stars, Be-star (rapidly rotating blue star with emission lines from a dense surrounding disc) with a neutron star in a highly elliptical orbit, who repeatedly comes close enough to the Be star to pick off some mattre and emit X-rays.

        As per the article a few days ago about BeX pulsars.

      3. That would be a rather small kick. They say in the article that their movement through the galaxy is much too slow. It makes you think that a binary could accelerate somewhere…what would be a huge kick and preferred direction? Could it shoot against the rotation of The Milky Way or towards center or out? 😀

      4. Expected kicks are from no kick up to 50-200km /sec. If the secondary is sufficiently massive, and the exploding primary is close enough, the kicked neutron star may very well still remain in the system. The actuall kick will affect the entire system (obviously, if they remain attached as the center of mass will move along the kick).

        Just ponder that if the sun weighed 15Msun, the escape speed for earth would require a 200km/sec ‘kick’.

        Solitary neutron star wanderers may eventually wander quite far off. Ofc, not all solitary neutron stars move at great speed, but some do.

      5. Thanks, I wondered if it was that, in the larger context. Also, I am glad to see so many helpful hands!

    2. A ‘dark collapse’ may be one of the end-types for massive stars, above something like 40 Msun IMF (Initial Mass Function) up to about 130Msun IMF. Although exact values for mass are variously uncertain, the following is a brief description for stars near the end of their lives:
      1. Stars 10-20 Msun IMF collapse to form a neutron star, the rebound of the neutron star sends a shockwave into the remainder of the star and initiates a SNe, and might also be the cause of an unsymmetrical kick that sends it careening.
      2. Stars 20-40 Msun IMF collapse first to form a neutron star, sending a shockwave and giving a kick in the same way as 1., but then the neutron star becomes unable to withstand the weight of the infalling matter and collapses again to form a black hole
      3. Stars 40-130 Msun IMF may collapse directly to a black hole, and the collapse may swallow the full effect of what would otherwise be a SNe. This is the ‘dark collaps’. No explosion, no kick (or at least much less kick). This is very uncertain, and it might be that some stars explode, some just collapse, depending on rotation etc.
      4. Stars with higher mass than 139Msun (and low metallicity and slow rotation) have yet another possible explosion mechanism, called pair-instability, wich makes the entire star explode into pieces.
      5. IF stars can become as massive as 300Msun or higher, they might also simply collapse directly to form a black hole.

    3. If a star is massive enough the gravitational implosion can continue to compress the material in spite of runaway fusion that occurs. So the nuclear processes which generate a supernova are present, but the gravitational collapse for a hefty star ~> 50M_{sol} is sufficient to compress the material further by overcoming the thermal pressure due to the energy release from fusion. This will implode the star into a black hole without a spectacular supernova event.


  2. It is interesting that they were able to make this characterization of the BH. The spin rate is fast, but nowhere near the extremal limit. A quick calcuation reveals the spin is only a few percent of the mass-energy.


  3. No information can escape the thing but it’s mass can still be ascertained.
    Very interesting and yet another indicator that gravity is an entirely different regime than energy.
    I wonder how they derived the spin-rate? X-ray pulses in the inner disk?

    What is the orbital period of the binary pair and the distance between them?
    How fast will it spin up when it finally gobbles the companion?
    Does it just sit there and generate questions?

    1. Gravity is an interaction that modify energy, it “is” not energy.

      Energy is a measure of the ability to do work on a system. Gravity is but one of several interactions that by definition do work.

    2. The black hole wont be able to gobble up the primary, because the primary will end its ‘life’ long before that. Within only a few million years, the primary (HDE 226868 ) will collapse and explode as a supernova, likely generating a black hole, but not as likely that it just collapses without an SNe event.

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