Top views of the Milky Way show sim­u­lat­ed data (left) and the observed posi­tions of the Cephei­ds.

J. Skowron/OGLE/Astronomical Obser­va­to­ry, Uni­ver­si­ty of War­saw

We don’t have a GPS sys­tem for our “warped and twist­ed” galaxy so astronomers have to get crafty when it comes to pin­point­ing our loca­tion among the stars and cre­at­ing maps of the Milky Way. We’ve seen epic cos­mic car­tog­ra­phy before, thanks to the Euro­pean Space Agen­cy’s Gaia space­craft. And now astronomers from the US and Europe have put togeth­er a new 3D mod­el of the galaxy based on the dis­tance between stars.

The research, pub­lished Thurs­day in the jour­nal Sci­ence, draws on a pop­u­la­tion of stars known as the Cephei­ds, which are puls­ing, mas­sive, young stars that shine brighter than the sun. Using data from the Opti­cal Grav­i­ta­tion­al Lens­ing Exper­i­ment (OGLE), a sky sur­vey run by the Uni­ver­si­ty of War­saw out of Las Cam­panas Obser­va­to­ry in Chile, astronomers were able to pick out 2,431 of the Cephei­ds through the thick gas and dust of the Milky Way and use them to make a map of the galaxy.

Doro­ta Skowron, lead author on the study and astronomer with Wro­claw Uni­ver­si­ty of Sci­ence and Tech­nol­o­gy, says the OGLE project observed the galac­tic disk of the Milky Way for six years, tak­ing 206,726 images of the sky con­tain­ing 1,055,030,021 stars. With­in, they found the pop­u­la­tion of Cephei­ds, which are par­tic­u­lar­ly use­ful for plot­ting a map because their bright­ness fluc­tu­ates over time.

This allows sci­en­tists to observe how bright the star is in real­i­ty ver­sus how bright it looks to us from Earth. The dif­fer­ence between these can tell us how far away a star might be from our sun.

Each col­ored point relates to a star in the Milky Way. The sun is des­ig­nat­ed by the spiked yel­low cir­cle. 

J. Skowron/OGLE/Astronomical Obser­va­to­ry, Uni­ver­si­ty of War­saw

Using that fluc­tu­a­tion, the team pro­duced a 3D mod­el of the galaxy, con­firm­ing work that pre­vi­ous­ly demon­strat­ed the galaxy was flared at its edges. They were also able to deter­mine the age of the Cepheid pop­u­la­tion, with younger stars locat­ed clos­er to the cen­ter of the galac­tic disk and old­er stars posi­tioned far­ther away, near the edge.

By sim­u­lat­ing star for­ma­tion in the ear­ly Milky Way, the team showed how the galaxy might have evolved over the last 175 mil­lion years, with bursts of star for­ma­tion in the spi­ral arms result­ing in the cur­rent dis­tri­b­u­tion of Cephei­ds rang­ing from 20 mil­lion to 260 mil­lion years old.

“We hope that our paper will be a very good start­ing point for more sophis­ti­cat­ed mod­el­ing of the Galaxy’s past,” says Skowron. “Our Cephei­ds are a great test­bed for check­ing the reli­a­bil­i­ty of such mod­els.”

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The new research fol­lows a study Nature Astron­o­my pub­lished in Feb­ru­ary. That study looked at 1,339 Cephei­ds and cre­at­ed one of the most com­pre­hen­sive 3D maps of the Milky Way, which showed that our home galaxy is twist­ed at its edges. It also used a slight­ly dif­fer­ent data set, specif­i­cal­ly look­ing at stars from one of NASA’s tele­scopes known as the Wide-field Infrared Sur­vey Explor­er (WISE).

The two stud­ies show very sim­i­lar results, par­tic­u­lar­ly in regard to the strange nature of the Milky Way’s warped edges. How­ev­er, there are still ques­tions about that phe­nom­e­non.

Richard de Gri­js, an astronomer at Mac­quar­ie Uni­ver­si­ty and co-author on the Nature Astron­o­my study, said that both the pre­vi­ous study and the new study rely on Cephei­ds that sit on our side of the Milky Way.

“A key ques­tion would be whether there is a sim­i­lar, pos­si­bly oppo­site warp [on the oth­er side] too,” he said.

If we could ana­lyze that oth­er side, we’d have a clear­er pic­ture of how the Milky Way’s strange warped edges came to be. Was it because of a merg­er with a small­er galaxy? Or because of grav­i­ta­tion­al effects? Skowron does­n’t believe that see­ing the oth­er side will dra­mat­i­cal­ly increase the num­ber of Cephei­ds they find. Projects like the Euro­pean Space Agen­cy’s Gaia, which con­tin­ues to sur­vey the entire Milky Way, may pro­vide a more con­crete answer.

Skowron notes that future projects will look at the old­er pop­u­la­tion of stars but also take into account anoth­er type of puls­ing star found in the galaxy — the RR Lyrae. These elder­ly stars are from a time much ear­li­er in the Milky Way’s life cycle, so they would pro­vide anoth­er method to map the galaxy.

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