Black hole may have sent star cluster hurtling toward Earth

Scientists believe they've found the fastest-approaching object in the universe

Topics: Scientific American, Black Hole, Earth, Star Cluster, Universe, , ,

Black hole may have sent star cluster hurtling toward Earth
This article was originally published by Scientific American.

Scientific American Most of the universe is rushing away from us. It’s not that we’re particularly repellent; it’s just that the universe is expanding, pushing most other galaxies away. Light from distant galaxies travels toward us through this expanding space, which stretches their light to longer, or redder, wavelengths. As a result, the spectra of most galaxies exhibit redshifts.

Now astronomers have accidentally discovered the greatest blueshift ever seen, in a star cluster that a giant black hole may have catapulted our way.

Over small distances gravity has reversed the universe’s expansion, so modest blueshifts are common. Neither the solar system nor the galaxy is expanding. Not even the Local Group—the collection of approximately 75 galaxies that includes the Milky Way—expands. In fact, the Local Group’s largest member, the Andromeda Galaxy, is moving toward us: it has a blueshift of 300 kilometers per second.

Yet astronomers have spotted an object far beyond the Local Group’s borders with a blueshift of 1,026 kilometers per second, far surpassing the previous record of 780 kps set by a star in the Andromeda Galaxy. “It’s always fun to be at the extreme,” says Nelson Caldwell, an astronomer at the Harvard–Smithsonian Center for Astrophysics who made not just this discovery but the earlier one as well. “That was a complete accident, too!”

Astronomers have recorded greater velocities when jets or explosions shoot debris toward us but they’ve never seen the main body of any star, star cluster or galaxy exhibit such an extreme blueshift.

Caldwell and his colleagues were measuring Doppler shifts of star clusters around M87, a giant elliptical galaxy located at the heart of the Virgo Cluster, 54 million light-years from Earth. Unlike the Local Group, which holds only two giant galaxies—Andromeda and our own Milky Way—the Virgo cluster has dozens of large galaxies. M87 possesses an enormous number of tightly packed star clusters called globulars. Whereas the Milky Way has about 160 known globular clusters M87 boasts some 10,000. Moreover, M87′s center has a black hole that dwarfs the Milky Way’s,weighing six billion to seven billion times more than the sun, over a thousand times as massive as the four-million–solar mass black hole occupying the Milky Way’s center.

In 2005 astronomers reported finding a so-called hypervelocity star that the Milky Way’s central black hole had kicked away. According to an idea proposed two decades earlier, when a binary star system skirts close enough to a black hole, one star falls in, losing a large amount of energy; in order to conserve energy, the other star shoots away at high speed.

A different three-body scenario may explain what Caldwell’s team calls the first hypervelocity globular cluster. If M87′s black hole actually consists of two black holes orbiting each other, they could fling away a star cluster that strayed too near. The cluster’s gravity causes the two black holes to get a little closer together, making them lose orbital energy that gets transferred to the star cluster. If it rushes away in our direction, it can acquire a large blueshift even though the galaxy it sprung from has a redshift of 1,307 kilometers per second. The astronomers have submitted their work to The Astrophysical Journal Letters.

“It’s a very interesting object,” says Daniel Batcheldor, an astronomer at the Florida Institute of Technology who is not affiliated with the researchers. “We do suspect that there has been a binary black hole at the center of M87 in the past but we don’t think that there’s one right now.” A binary black hole can arise after two large galaxies, each with their own black holes, smash together. Furthermore, such galaxy mergers would explain M87′s gargantuan size. When its central black hole was still two separate supermassive black holes, it could have hurled the star cluster away. But Batcheldor says the blueshifted object may instead be a dwarf galaxy on the far side of M87 that is plunging into the galaxy, explaining its high velocity toward us.

Additional observations are vital. “To really nail down that it’s been ejected from M87, we would like to know its distance,” Caldwell says. The Hubble Space Telescope can glimpse the cluster’s brightest stars, which will reveal how far it is. If it’s closer than M87, that would favor the ejection scenario.

Despite its extreme blueshift, the object won’t hit us, because it surely has some sideways motion. But it faces a lonely future. “This thing will eventually leave Virgo and then be in between clusters of galaxies,” Caldwell says. “If it really was ejected by some binary black hole mechanism, then there probably should be a few more. We’re certainly going to keep looking.”

More Related Stories

Featured Slide Shows

  • Share on Twitter
  • Share on Facebook
  • 1 of 11
  • Close
  • Fullscreen
  • Thumbnails

    Ten spectacular graphic novels from 2014

    Beautiful Darkness by Fabien Vehlmann & Kerascoët
    Kerascoët's lovely, delicate pen-and-watercolor art -- all intricate botanicals, big eyes and flowing hair -- gives this fairy story a deceptively pretty finish. You find out quickly, however, that these are the heartless and heedless fairies of folk legend, not the sentimental sprites beloved by the Victorians and Disney fans. A host of tiny hominid creatures must learn to survive in the forest after fleeing their former home -- a little girl who lies dead in the woods. The main character, Aurora, tries to organize the group into a community, but most of her cohort is too capricious, lazy and selfish to participate for long. There's no real moral to this story, which is refreshing in itself, beyond the perpetual lessons that life is hard and you have to be careful whom you trust. Never has ugly truth been given a prettier face.

    Ten spectacular graphic novels from 2014

    Climate Changed: A Personal Journey Through the Science by Philippe Squarzoni
    Squarzoni is a French cartoonist who makes nonfiction graphic novels about contemporary issues and politics. While finishing up a book about France under Jacques Chirac, he realized that when it came to environmental policy, he didn't know what he was talking about. "Climate Changed" is the result of his efforts to understand what has been happening to the planet, a striking combination of memoir and data that ruminates on a notoriously elusive, difficult and even imponderable subject. Panels of talking heads dispensing information (or Squarzoni discussing the issues with his partner) are juxtaposed with detailed and meticulous yet lyrical scenes from the author's childhood, the countryside where he takes a holiday and a visit to New York. He uses his own unreachable past as a way to grasp the imminent transformation of the Earth. The result is both enlightening and unexpectedly moving.

    Ten spectacular graphic novels from 2014

    Here by Richard McGuire
    A six-page version of this innovative work by a regular contributor to the New Yorker first appeared in RAW magazine 25 years ago. Each two-page spread depicts a single place, sometimes occupied by a corner of a room, over the course of 4 billion years. The oldest image is a blur of pink and purple gases; others depict hazmat-suited explorers from 300 years in the future. Inset images show the changing decor and inhabitants of the house throughout its existence: family photos, quarrels, kids in Halloween costumes, a woman reading a book, a cat walking across the floor. The cumulative effect is serene and ravishing, an intimation of the immensity of time and the wonder embodied in the humblest things.

    Ten spectacular graphic novels from 2014

    Kill My Mother by Jules Feiffer
    The legendary Pulitzer Prize-winning cartoonist delivers his debut graphic novel at 85, a deliriously over-the-top blend of classic movie noir and melodrama that roams from chiaroscuro Bay City to Hollywood to a USO gig in the Pacific theater of World War II. There's a burnt-out drunk of a private eye, but the story is soon commandeered by a multigenerational collection of ferocious women, including a mysterious chanteuse who never speaks, a radio comedy writer who makes a childhood friend the butt of a hit series and a ruthless dame intent on making her whiny coward of a husband into a star. There are disguises, musical numbers and plenty of gunfights, but the drawing is the main attraction. Nobody convey's bodies in motion more thrillingly than Feiffer, whether they're dancing, running or duking it out. The kid has promise.

    Ten spectacular graphic novels from 2014

    The Motherless Oven by Rob Davis
    This is a weird one, but in the nervy surreal way that word-playful novels like "A Clockwork Orange" or "Ulysses" are weird. The main character, a teenage schoolboy named Scarper Lee, lives in a world where it rains knives and people make their own parents, contraptions that can be anything from a tiny figurine stashable in a pocket to biomorphic boiler-like entities that seem to have escaped from Dr. Seuss' nightmares. Their homes are crammed with gadgets they call gods and instead of TV they watch a hulu-hoop-size wheel of repeating images that changes with the day of the week. They also know their own "death day," and Scarper's is coming up fast. Maybe that's why he runs off with the new girl at school, a real troublemaker, and the obscurely dysfunctional Castro, whose mother is a cageful of talking parakeets. A solid towline of teenage angst holds this manically inventive vision together, and proves that some graphic novels can rival the text-only kind at their own game.

    Ten spectacular graphic novels from 2014

    NOBROW 9: It's Oh So Quiet
    For each issue, the anthology magazine put out by this adventurous U.K.-based publisher of independent graphic design, illustration and comics gives 45 artists a four-color palette and a theme. In the ninth issue, the theme is silence, and the results are magnificent and full of surprises. The comics, each told in images only, range from atmospheric to trippy to jokey to melancholy to epic to creepy. But the two-page illustrations are even more powerful, even if it's not always easy to see how they pertain to the overall concept of silence. Well, except perhaps for the fact that so many of them left me utterly dumbstruck with visual delight.

    Ten spectacular graphic novels from 2014

    Over Easy by Mimi Pond
    When Pond was a broke art student in the 1970s, she took a job at a neighborhood breakfast spot in Oakland, a place with good food, splendid coffee and an endlessly entertaining crew of short-order cooks, waitresses, dishwashers and regular customers. This graphic memoir, influenced by the work of Pond's friend, Alison Bechdel, captures the funky ethos of the time, when hippies, punks and disco aficionados mingled in a Bay Area at the height of its eccentricity. The staff of the Imperial Cafe were forever swapping wisecracks and hopping in and out of each other's beds, which makes them more or less like every restaurant team in history. There's an intoxicating esprit de corps to a well-run everyday joint like the Imperial Cafe, and never has the delight in being part of it been more winningly portrayed.

    Ten spectacular graphic novels from 2014

    The Shadow Hero by Gene Luen Yang and Sonny Liew
    You don't have to be a superhero fan to be utterly charmed by Yang and Liew's revival of a little-known character created in the 1940s by the cartoonist Chu Hing. This version of the Green Turtle, however, is rich in characterization, comedy and luscious period detail from the Chinatown of "San Incendio" (a ringer for San Francisco). Hank, son of a mild-mannered grocer, would like to follow in his father's footsteps, but his restless mother (the book's best character and drawn with masterful nuance by Liew) has other ideas after her thrilling encounter with a superhero. Yang's story effortlessly folds pathos into humor without stooping to either slapstick or cheap "darkness." This is that rare tribute that far surpasses the thing it celebrates.

    Ten spectacular graphic novels from 2014

    Shoplifter by Michael Cho
    Corinna Park, former English major, works, unhappily, in a Toronto advertising agency. When the dissatisfaction of the past five years begins to oppress her, she lets off steam by pilfering magazines from a local convenience store. Cho's moody character study is as much about city life as it is about Corinna. He depicts her falling asleep in front of the TV in her condo, brooding on the subway, roaming the crowded streets after a budding romance goes awry. Like a great short story, this is a simple tale of a young woman figuring out how to get her life back, but if feels as if it contains so much of contemporary existence -- its comforts, its loneliness, its self-deceptions -- suspended in wintery amber.

    Ten spectacular graphic novels from 2014

    Through the Woods by Emily Carroll
    This collection of archetypal horror, fairy and ghost stories, all about young girls, comes lushly decked in Carroll's inky black, snowy white and blood-scarlet art. A young bride hears her predecessor's bones singing from under the floorboards, two friends make the mistake of pretending to summon the spirits of the dead, a family of orphaned siblings disappears one by one into the winter nights. Carroll's color-saturated images can be jagged, ornate and gruesome, but she also knows how to chill with absence, shadows and a single staring eye. Literary readers who cherish the work of Kelly Link or the late Angela Carter's collection, "The Bloody Chamber," will adore the violent beauty on these pages.

  • Recent Slide Shows


Loading Comments...