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Giant bubbles found at heart of Milky Way

Nov. 9, 2010
Courtesy of NASA
and World Science staff

A NASA space tel­e­scope has un­veiled a gi­ant, pre­vi­ously un­seen struc­ture re­sem­bling a pair of gi­ant bub­bles at the cen­ter of our Milky Way gal­axy, as­tro­no­mers say. 

The fea­ture spans 50,000 light-years, or about half the width of the gal­axy it­self, and may be the rem­nant of an erup­tion from a su­per­sized black hole at the cen­ter of our gal­axy, they add.

This artist's il­lus­tra­tion de­picts the ap­prox­i­mate way as­tro­no­mers be­lieve new­ly iden­ti­fied, gi­ant bub­bles in the Milky Way would look to an ob­serv­er out­side the gal­axy, if their light were vis­i­ble. (Cour­te­sy NA­SA GSFC)

“What we see are two gam­ma ray-emitting bub­bles that ex­tend 25,000 light-years north and south of the ga­lac­tic cen­ter,” above and be­low the ga­lac­tic disc it­self, said Doug Finkbeiner, an as­tron­o­mer at the Har­vard-Smithsonian Cen­ter for As­t­ro­phys­ics in Cam­bridge, Mass. “We don’t fully un­der­stand their na­ture or ori­gin.” 

The struc­ture spans more than half the vis­i­ble sky, from the con­stella­t­ion Vir­go to the con­stella­t­ion Grus, and it may be mil­lions of years old, Finkbeiner and col­leagues said. A pa­per on the find­ings, based on re­search us­ing NASA’s Fer­mi Gam­ma-ray Space Tel­e­scope, has been ac­cept­ed for pub­lica­t­ion in The As­t­ro­phys­i­cal Jour­nal.

Finkbeiner and Har­vard grad­u­ate stu­dents Meng Su and Tra­cy Slatyer said they dis­cov­ered the bub­bles by pro­cess­ing pub­licly avail­a­ble da­ta from the ob­serv­a­to­ry, which has the most sen­si­tive gam­ma-ray de­tec­tor ev­er launched. Gam­ma rays are the highest-en­er­gy form of light, invis­i­ble to the un­aided eye.

The bub­bles had elud­ed pre­vi­ous de­tec­tion partly be­cause of a fog of gam­ma rays that ap­pears through­out the sky, ac­cord­ing to Fink­beiner and col­leagues. This fog, they said, arises when par­t­i­cles mov­ing near the speed of light in­ter­act with light and gas in the Milky Way. Re­search­ers us­ing the tel­e­scope con­stantly re­fine mod­els to un­cov­er new sources of gam­ma-ray light ob­scured by this so-called dif­fuse emis­sion. By us­ing var­i­ous es­ti­mates of the fog, Fink­beiner and his col­leagues said they iso­lat­ed it from the tel­e­scope da­ta and un­veiled the gi­ant bub­bles.

Sci­en­tists are con­duct­ing more anal­y­ses to find out how the struc­ture was formed. 

The bub­ble emis­sions are de­scribed as hav­ing well-de­fined edges. The struc­ture’s shape and emis­sions sug­gest it was formed as a re­sult of a large, rel­a­tively fast en­er­gy re­lease — from where, no one knows, re­search­ers added. One pos­si­bil­ity in­cludes a par­t­i­cle je­t from the “su­per­mas­sive” black hole at the ga­lac­tic cen­ter. A black hole is a super-compact ob­ject that is so heavy that its gra­vity draws in even light.

In many oth­er ga­lax­ies, as­tro­no­mers see fast par­t­i­cle je­ts pow­ered by mat­ter fall­ing to­ward a cen­tral black hole. While there is no ev­i­dence the Milky Way’s black hole has such a je­t to­day, it may have in the past, re­search­ers said. The bub­bles al­so may have formed as a re­sult of gas out­flows from a burst of star forma­t­ion, per­haps the one that pro­duced many mas­sive star clus­ters in the Milky Way’s cen­ter sev­eral mil­lion years ago, some spec­u­lat­ed.

“In oth­er ga­lax­ies, we see that star­bursts can drive enor­mous gas out­flows,” said Da­vid Sper­gel, a sci­ent­ist at Prince­ton Uni­vers­ity. “Whatev­er the en­er­gy source be­hind these huge bub­bles may be, it is con­nect­ed to many deep ques­tions in as­t­ro­phys­ics.”

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A NASA space telescope has unveiled a giant, previously unseen structure resembling a pair of giant bubbles at the center of our Milky Way galaxy, astronomers say. The feature spans 50,000 light-years, or about half the width of the galaxy itself, and may be the remnant of an eruption from a supersized black hole at the center of our galaxy, they add. “What we see are two gamma ray-emitting bubbles that extend 25,000 light-years north and south of the galactic center,” above and below the galactic disc itself, said Doug Finkbeiner, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. “We don’t fully understand their nature or origin.” The structure spans more than half the visible sky, from the constellation Virgo to the constellation Grus, and it may be millions of years old, Finkbeiner and colleagues said. A paper on the findings, based on research using NASA’s Fermi Gamma-ray Space Telescope, has been accepted for publication in The Astrophysical Journal. Finkbeiner and Harvard graduate students Meng Su and Tracy Slatyer said they discovered the bubbles by processing publicly available data from the observatory, which has the most sensitive and gamma-ray detector ever launched. Gamma rays are the highest-energy form of light, invisible to the unaided eye. The bubbles had eluded previous detection partly because of a fog of gamma rays that appears throughout the sky, according to Finkbeiner and colleagues. This fog, they said, arises when particles moving near the speed of light interact with light and gas in the Milky Way. Researchers using the telescope constantly refine models to uncover new sources of gamma-ray light obscured by this so-called diffuse emission. By using various estimates of the fog, Finkbeiner and his colleagues said they isolated it from the telescope data and unveiled the giant bubbles. Scientists are conducting more analyses to find out how the structure was formed. The bubble emissions are described as having well-defined edges. The structure’s shape and emissions suggest it was formed as a result of a large, relatively fast energy release — from where, no one knows, researchers added. One possibility includes a particle jet from the “supermassive” black hole at the galactic center. A black hole is a super-compact object that is so heavy that its gravity draws in even light. In many other galaxies, astronomers see fast particle jets powered by matter falling toward a central black hole. While there is no evidence the Milky Way’s black hole has such a jet today, it may have in the past, researchers said. The bubbles also may have formed as a result of gas outflows from a burst of star formation, perhaps the one that produced many massive star clusters in the Milky Way’s center several million years ago, some speculated. “In other galaxies, we see that starbursts can drive enormous gas outflows,” said David Spergel, a scientist at Princeton University. “Whatever the energy source behind these huge bubbles may be, it is connected to many deep questions in astrophysics.”