Media Releases

In the dragonfish’s mouth: the next generation of superstars to stir up our galaxy

November 30, 2011

TORONTO, ON — Three astronomers at the Uni­ver­si­ty of Toron­to have found the most numer­ous batch of young, super­mas­sive stars yet observed in our galaxy: hun­dreds of thou­sands of stars, includ­ing sev­er­al hun­dreds of the most mas­sive kind –blue stars dozens of times heav­ier than our Sun. The light these new­born stars emit is so intense it has pushed out and heat­ed the gas that gave them birth, carv­ing out a glow­ing hol­low shell about a hun­dred light-years across.

These find­ings will be pub­lished in the Decem­ber 20 issue of Astro­phys­i­cal Jour­nal Let­ters. For the researchers, the next step is already clear: “By study­ing these super­mas­sive stars and the shell sur­round­ing them, we hope to learn more about how ener­gy is trans­mit­ted in such extreme envi­ron­ments,” says Mub­di Rah­man, a PhD can­di­date in the Depart­ment of Astron­o­my & Astro­physics at the Uni­ver­si­ty of Toron­to, who led the work with his super­vi­sors, Pro­fes­sors Dae-Sik Moon and Christo­pher Matzn­er.

Such large nurs­eries of mas­sive stars have been noticed in oth­er galax­ies, but were so far away that all stars are often blurred togeth­er on images tak­en by tele­scopes. “This time, the mas­sive stars are right here in our galaxy, and we can even count them indi­vid­u­al­ly,” Rah­man says.

Study­ing the indi­vid­ual stars will require intri­cate mea­sure­ments. The clus­ter of bright stars is locat­ed near­ly halfway across our galaxy, 30,000 light-years away, and the line of sight is blocked by dust. “All this dust made it dif­fi­cult for us to fig­ure out what type of stars they are,” Rah­man says.

“These stars are incred­i­bly bright,” Rah­man says, “yet, they’re very hard to see.” Before the light from these stars can reach us, most of it is absorbed by the inter­ven­ing dust in our galaxy. This makes the bright­est stars in the clus­ter appear as dim as small­er, near­by stars. The fainter stars in the clus­ter appear so dim that they are not seen.

The researchers used the New Tech­nol­o­gy Tele­scope at the Euro­pean South­ern Obser­va­to­ry in Chile to col­lect what­ev­er light they could from a few dozen stars. They mea­sured in details how much light the stars emit in each colour, and were final­ly able to con­firm that at least a dozen stars in the clus­ter were of the most mas­sive kind, some pos­si­bly a hun­dred times more mas­sive than our Sun.

In fact, before turn­ing a ground tele­scope toward the stars them­selves, Rah­man first noticed the glow from the large shell of heat­ed gas using the WMAP satel­lite, which is sen­si­tive to microwaves (between radio waves and vis­i­ble light). To make an image of the gas shell being blown away and heat­ed up, the researchers used the Spitzer satel­lite, which works with infrared light (between microwave and vis­i­ble light).

Rah­man sug­gest­ed the name “Drag­on­fish” after com­par­ing the infrared image of the celes­tial gas shell with Peter Shearer’s illus­tra­tion of the deep-sea crea­ture with the same name. The astro­nom­i­cal image resem­bles a dark gap­ing mouth-like shape with teeth, two eyes, and a bright fin to the right. The “mouth” is the vol­ume from which the gas has been cleared by the light of the stars, pushed out­ward to form a shell that is par­tic­u­lar­ly bright in spots cor­re­spond­ing to the eyes and the fin of the ani­mal.

“We were able to see the effect of the stars on their sur­round­ings before see­ing the stars direct­ly”, Rah­man says. This would be like see­ing lit faces and red cheeks from the heat of a camp­fire, with­out being able to see the logs and flames them­selves.

In the same way that red embers are cool­er than the blue flame of a weld­ing torch, the gas is cool­er than what is heat­ing it, and thus glows red­der than the blue stars. Com­pared to the colours of a rain­bow rang­ing from red to blue, most of the light emit­ted by the heat­ed gas is in fact red­der than red, and thus infrared –less affect­ed by gas or dust, and invis­i­ble to our naked eyes, but not to appro­pri­ate tele­scope instru­ments. At the oth­er end of the rain­bow, the giant stars in the clus­ter are bluer than blue, and emit most­ly in the ultra­vi­o­let, which is blocked by dust and thus not vis­i­ble on the image.

“But we had to make sure what was at the heart of the shell,” Rah­man says. Now that the astronomers have iden­ti­fied sev­er­al stars there as very mas­sive, they know that these stars will burn their nuclear fuel rel­a­tive­ly quick­ly in astro­nom­i­cal terms: with­in a few mil­lion years (thou­sands of times faster than for our Sun) even though the giant blue stars con­tain dozens of times more fuel than our Sun.

“Still, if you thought the inside of the shell was emp­ty, think again,” Rah­man says. For each of the few hun­dred super­stars the researchers may have spot­ted, there are thou­sands of aver­age stars more akin to our Sun. When the super­stars have burned through their fuel, they will explode and release met­als and oth­er heavy atoms that may help form rocky plan­ets around small­er, qui­eter stars –per­haps pro­vid­ing the build­ing blocks for life.

“There may be new­er stars already form­ing in the eyes of the Drag­on­fish,” Rah­man says. Some areas in the shell glow par­tic­u­lar­ly bright, and the researchers think the gas there may have been com­pressed enough to ignite even more stars.

The gas now in the shell is the remain­der of the very gas that gave birth to the stars, and there is a lot of it: the moth­er shell is more mas­sive than the clus­ter of its babies. But with no moth­er any­more  to keep them reined in via its mass and grav­i­ty, all the young stars may start wan­der­ing off in all direc­tions. “We’ve found a rebel in the group, a run­away star escap­ing from the group at high speed,” Rah­man says. “We think the group is no longer tied togeth­er by grav­i­ty: how­ev­er, how the asso­ci­a­tion will fly apart is some­thie still don’t under­stand well.”

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ADDITIONAL MEDIA:

A high-res­o­lu­tion infrared image of Drag­on­fish asso­ci­a­tion, show­ing the shell of hot gas, can be found at:

http://dl.dropbox.com/u/34618436/Images/Dragonfish_Association_Rahman.jpg

This image can be reused freely, pro­vid­ed the fol­low­ing cred­its are dis­played clear­ly: NASA/J­PL-Cal­tech/GLIMPSE Team/Mubdi Rah­man

The high-res­o­lu­tion illus­tra­tion of the ani­mal, cre­at­ed by Peter Shear­er after dig­i­tal­ly alter­ing his pho­to of a dead Black Drag­on­fish (with left and right flipped for con­ve­nience), can be down­loaded from:

http://dl.dropbox.com/u/34618436/Images/Dragonfish_Shearer_Flipped.jpg

This image can be reused freely, pro­vid­ed the fol­low­ing cred­its are dis­played clear­ly: Peter Shear­er, www.petershearer.co.nz

The online ver­sion of the sci­en­tif­ic paper can be down­loaded from:

http://iopscience.iop.org/2041–8205/743/2/L28

For more infor­ma­tion, please con­tact:

Mub­di Rah­man
Depart­ment of Astron­o­my & Astro­physics, Uni­ver­si­ty of Toron­to
416–893-7641
rahman@astro.utoronto.ca

Prof. Dae-Sik Moon
Depart­ment of Astron­o­my & Astro­physics, Uni­ver­si­ty of Toron­to
416–978-6566
moon@astro.utoronto.ca

Prof. Christo­pher Matzn­er
Depart­ment of Astron­o­my & Astro­physics
Uni­ver­si­ty of Toron­to
416–978-2172
matzner@astro.utoronto.ca

Johannes Hirn, PhD
Com­mu­ni­ca­tions, Dun­lap Institue for Astron­o­my & Astro­physics
Uni­ver­si­ty of Toron­to
416–525-6329
hirn@di.utoronto.ca