What Will Happen When Black Holes Collide?



If one wasn’t enough to baffle the scientists, imagine a double whammy!! Collision of black holes. For more than 20 years, astronomers have considered an intriguing question: What happens when two black holes meet? Inside a galaxy, black holes that formed from dead, massive stars might encounter each other, especially in double or multiple star systems. No one has yet seen such a collision take place, but the subject is becoming a hot topic of theoretical astrophysics.

Studying the possibilities took a big step forward in 2004, when a team of astronomers — Marc Favata of Cornell University, Scott Hughes of the Massachusetts Institute of Technology, and Daniel Holz of the University of Chicago — authored a study that appeared in Astrophysical Journal Letters; this kicked off a number of other studies to create a burgeoning field. It turns out astronomers think a funny thing happens when black holes collide. They spiral toward each other and merge into a single entity. A gravitational “sling- shot” effect then violently whips them outside their host galaxies into intergalactic space.

The ejection mechanism results from a byproduct of the merger: gravitational waves. The gravitational waves actually shoot the merged black hole far away from the site of its merger. What role does this process play in building black holes? Could large numbers of black holes exist outside galaxies, where their presence would be extremely difficult to detect? These questions and others are currently on the table, and researchers are looking to build their knowledge of the subject.

A real breakthrough would come from observing a binary black hole — a black-hole merger in the making. “Almost all large galaxies contain black holes,” says Hughes, “and galaxies merge like mad — especially a couple billion years ago.” Hughes believes binary black holes could have formed and be forming yet today, but detecting them observationally will be difficult. “We’re talking about two incredibly small bodies separated by a parsec,” he says, merely 3.26 light-years in galaxies that span hundreds of thousands of light years across. Black holes escaping their parent galaxies would be shot out at high velocities, probably 685,000 mph (1.1 million km/h). Such high-speed objects eventually might join other nomadic black holes in deep space. Such freeform black holes would prove elusive.

“If they’re not shining [from radiation produced by swallowing nearby bright material], it’s hard to know where to look,” according to Piero Madau of the University of California, Santz Cruz. The only way to detect intergalactic black holes would be from gravitational-lensing effects, and current telescopes are unable to do that. Intergalactic black holes could absorb material without radiating, and so, continue along below the radar. “For that reason,” says Mitch Begelman of the University of Colorado, “We can’t rule out the possibility that black holes outside galaxies contain more mass than black holes inside galaxies.” The evidence for small black holes gone missing from normal galaxies does hold some potential.

According to David Merritt of the Rochester Institute of Technology in New York, “As we look at ever smaller galaxies, there’s a point where you stop seeing black holes.” Merritt and other astronomers wonder if smaller galaxies may have had their small stellar black holes shot out into intergalactic space.

Studying black-hole mergers could pay off big dividends when it comes to understanding large black holes in the early universe. Do they form by the process of mergers or by gradual accretion? Observational tests for determining how big black holes formed in the early cosmos are lacking; perhaps looking at how smaller black holes behave in more recent times will shed light on this question.


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  • Citation:Magnetic
    field reversal and jet speed variation
    contributing a reversiable magnetic field call for an acceleration and
    deceleration in Blackholes:

    Galaxies are thought to have
    formed from matter and energy that originated in the Big Bang, the theoretical
    explosion that started the expansion of the universe. How supermassive black
    holes formed at the center of active galaxies is under lively debate. The
    dominant school of thought is that matter clumped together to form stars during
    the initial phases of the first galaxies, and some stars were so large and
    dense that they could not withstand their own gravity and imploded to create
    black holes. Another school of thought, to which Vestergaard’s research has
    contributed, is that black holes came into being first and stars formed around
    them to create galaxies.

    Nandakumar,Oford astrophysicist says that temperature difference in condensed
    matter physics of space may call for a spring type reaction calling for
    magneticfield reversal under extreme temperature variations in understanding
    blackhole dynamics as energy rewinding and future radiation of evolution. in
    galaxies forming a blackhole. BH from a low-mass galaxy but is below the escape
    velocity from the Milky Way (MW) galaxy. If central BHs were common in the
    galactic building blocks that merged to make the MW, then numerous BHs that
    were kicked out of low-mass galaxies should be freely floating in the MW halo
    today. We use a large statistical sample of possible merger tree histories for
    the MW to estimate the expected number of recoiled BH remnants present in the
    MW halo today. We find that hundreds of BHs should remain bound to the MW halo
    after leaving their parent low-mass galaxies.

    The galaxies around these early
    supermassive black holes were very young, with intense star formation. Other
    astronomers have established that the mass of a black hole and the mass of its
    galaxy are strictly correlated. These data support the theory that early black
    holes formed first and galaxies formed around them. “But we need a lot more
    data on this to know for sure if this hypothesis is correct,” says Vestergaard

    Understanding this connection
    between stars in a galaxy and the growth of a black hole, and vice-versa, is the
    key to understanding how galaxies form throughout cosmic time”If a black
    hole is spinning it drags space and time with it and that drags the accretion
    disc, containing the black hole’s food, closer towards it. This makes the black
    hole spin faster, a bit like an ice skater doing a pirouette. A
    new way to measure supermassive black hole spin in accretion disc-dominated
    active galaxies Astronomers report the exciting discovery of a new way
    to measure the mass of super massive black holes in galaxies. By measuring
    the speed with which carbon monoxide molecules orbit around such black holes,
    this new research opens the possibility of making these measurements in many
    more galaxies than ever before. Supermassive black holes are now known to
    reside at the centres of all galaxies. In the most massive galaxies in the
    Universe, they are predicted to grow through violent collisions with other
    galaxies, which trigger the formation of stars and provides food for the black
    holes to devour. These violent collisions also produce dust within the galaxies
    therefore embedding the black hole in a dusty envelope for a short period of
    time as it is being fed. Galaxies with hidden supermassive black holes tend to
    clump together in space more than the galaxies with exposed, or unobscured,
    black holes. The Herschel Space Observatory has shown galaxies with the most
    powerful, active black holes at their cores produce fewer stars than galaxies
    with less active black holes. The results are the first to demonstrate black
    holes suppressed galactic star formation when the universe was less than half
    its current age. Galaxies with massive black holes were found to have high
    rates of star formation, with some forming stars at a thousand times the rate
    of our own Milky Way galaxy today. But intriguingly, the Herschel results show
    that the fastest-growing black holes are in galaxies with very little star
    formation – once the radiation coming from close to the black hole exceeds a
    certain power, it tends to “switch off” star formation in its galaxy.

    Gas falling toward a black hole spirals inward and piles up into an accretion
    disk, where it becomes compressed and heated. Near the inner edge of the disk,
    on the threshold of the black hole’s event horizon — the point of no return —
    some of the material becomes accelerated and races outward as a pair of jets
    flowing in opposite directions along the black hole’s spin axis. These jets
    contain particles moving at nearly the speed of light, which produce gamma rays
    — the most extreme form of light — when they interact.

    The idea is that low-mass proto-galaxies with
    black holes at their center would have merged, creating a gravitational kick
    that would send the now larger black hole outward fast enough to escape the
    host dwarf galaxy, but not fast enough to leave the overall galactic halo. Hubblesite.org
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