Media Releases

3D coming to a galaxy near you

June 22, 2011

TORONTO, ON — Astronomers usu­al­ly only see flat ver­sions of the real galax­ies in the Uni­verse, as pic­tures pro­ject­ed on their com­put­er screens. But researchers in the inter­na­tion­al col­lab­o­ra­tion ATLAS3D have used a clever trick to fig­ure out what 260 galax­ies do in the third dimen­sion miss­ing from their images.

They added motion to the pic­ture by mea­sur­ing the veloc­i­ties of stars going through the plane of the image. Using this method, the ATLAS3D researchers were able to tell whether stars were part of a flat­tened spin­ning disk or a motion­less bal­loon-shaped blob (called ellip­ti­cal galaxy).

This advance should help them fig­ure out how galax­ies change as they age and col­lide with one anoth­er.

Spi­rals, Disks, and Blobs

We’ve all seen pic­tures of spin­ning galax­ies with ele­gant spi­ral arms and dust lanes in-between their stars.

Even when seen edge-on, the dust lanes are vis­i­ble, so it’s easy to tell that these galax­ies have disks.

But some disk galax­ies have lit­tle gas or dust, or lack spi­ral arms. With­out such struc­tures, they appear as round­ed shapes when seen face-on, or oval ones when seen at an angle.

These fea­ture­less galax­ies can eas­i­ly be con­fused with ellip­ti­cal galax­ies, which are foot­ball-shaped, but bare­ly spin at all.

Tak­ing a Hit

By telling us how fast stars in a galaxy rotate around their galaxy’s cen­tre, the ATLAS3D result changes our under­stand­ing of galax­ies and how they evolve over time. Not only could the astronomers find out whether a foot­ball-shaped blob is a motion­less galaxy or a spin­ning disk, they can learn more about what hap­pens when galax­ies hit each oth­er.

Young galax­ies seem to have lots of gas that hasn’t yet been turned into burn­ing stars —and they spin fast, so they look like the poster-child galaxy with spi­ral arms and dust lanes.

As galax­ies col­lide or com­bine, they cause each other’s gas to spark into new stars. Old­er galax­ies have less gas, lit­tle dust, and no spi­ral arms.

More Than Meets the Eye

The ATLAS3D researchers found that, of those old­er galax­ies with­out spi­ral arms or dust lanes, many more did have a spin­ning disk struc­ture than pre­vi­ous­ly thought —even though they had been clas­si­fied as motion­less ellip­ti­cal galax­ies from their two-dimen­sion­al pic­ture.

These galax­ies have already been through col­li­sions, and if they have kept spin­ning, it may mean that col­li­sions do not ruin the order­ly rota­tion of their disks so much. The ATLAS3D team has already pre­pared com­put­er sim­u­la­tions and per­formed more tele­scope obser­va­tions to test this idea.

The ATLAS3D researchers used the 4.2‑m William Her­schel Tele­scope on La Pal­ma, Canary Islands, dur­ing 40 nights to make their obser­va­tions. They relied on the SAURON inte­gral-field spec­tro­graph to map out the speed of stars in 260 near­by galax­ies.



Dr. Anne-Marie Wei­j­mans
Dun­lap Insti­tute for Astron­o­my & Astro­physics
Uni­ver­si­ty of Toron­to

Dr. Michele Cap­pel­lari
Depart­ment of Physics
Uni­ver­si­ty of Oxford