Bars may kill spiral galaxies

About half of these spir als al so have a ba r, a straight struc ture cross ing the cen ter. Our own Milky Way gal­axy is a spir al with a small ba r.

Bars are be lieved to strongly in flu ence the ev o lu tion of ga lax ies as they pro vide a way to move ma te ri al in and out in the disk and pos sibly help to spark star forma t ion in the cen tral re gions. They may even help feed the cen tral mas sive black hole that seems to be pre s ent in al most all ga lax ies.

But sci en tists don’t un der stand why some ga lax ies have ba rs and oth ers don’t.

In the new stu dy, sci en tists drew on the work of vol­un teers for Gal axy Zoo 2, an on line proj ect in which mem bers of the pub lic are asked to care fully clas si fy ga lax ies shown in pho tos.

With these da ta — which they called the larg est ev er sam ple of ga lax ies with vis u al ba r iden ti fica t ions — the re search ers, led by cos mol o gist Ka ren Mas ters at the Uni vers­ity of Ports mouth in the U.K., de ter mined that red dish spir als are about twice as likely to host ba rs as blu ish spir als. This mat ters be cause col or is a clue to gal axy age. “Blue” ga lax ies get their hue from the hot young stars they con tain, im ply ing that they are form ing many stars and are young. In “red” ga lax ies, this star forma t ion has stopped, leav ing be hind the cool er, long-lived stars, which are red der.

The as tro no mers con clude that ba rs might help to kill spir al ga lax ies, al though how they do it re mains a mys tery. But the Milky Way has a ba r too, so the find ing may be tell ing us some thing about its fu ture.

In a state ment issued as the findings were revealed this week, Mas ters was n’t fo cus ing on any dis may she might feel for the pos sible aes thet ic de mise of our home gal axy. In­stead, she said it was “won der ful” to have “so many peo ple in volved in this re search.”

“I feel a great weight of re spon si bil ity to make sure good sci ence comes out of all the hard work they put in to clas si fying ga lax ies,” she added. Da ta hint ing at the new re sult has ex isted for “some time,” she went on, but “with such a large num ber of bar clas­sifica t ions we’re much more con fi dent about our re sults. And all of this is thanks to the dedica t ion of the vol un teers who pro vide the raw ‘clicks’.

“It’s not yet clear wheth er the ba rs are some side ef fect of an ex ter nal pro cess that turns spir al ga lax ies red, or if they alone can cause this trans forma t ion. We should get clos er to an swer ing that ques tion with more work on the Gal axy Zoo da taset.”

A pa per on the find ings is to ap pear in the jour nal Monthly No tices of the Roy al As tro­nom i cal So ci e ty and is al so posted on the on line da tabase arX iv.org.