“Our Milky Way Galaxy is Getting Bigger” –As Stars Form on the Galactic Outskirts

 
Eso-milky-way-3

 

"The Milky Way is pretty big already. But our work shows that at least the visible part of it is slowly increasing in size, as stars form on the galactic outskirts," says Cristina Martínez-Lombilla, a PhD candidate at the Instituto de Astrofísica de Canarias in Tenerife, Spain. "It won't be quick, but if you could travel forward in time and look at the galaxy in 3 billion years' time it would be about 5% bigger than today."


Our home galaxy consists of several hundred billion stars, with huge amounts of gas and dust, all intermingled and interacting through the force of gravity. The data from APEX was combined with the European Space Agency’s Planck satellite to provide an image above that is four times better than anything ever seen and is part of the ATLASGAL (APEX Telescope Large Area survey of the Galaxy).

 

The nature of this interaction determines the shape of a galaxy, which may be spiral, elliptical or irregular. As a barred spiral, the Milky Way consists of a disc in which stars, dust, and gas lie mostly in a flat plane, with arms stretching out from a central bar.

In the disc of the Milky Way there are stars of many different ages. Massive, hot, blue stars are very luminous and have a relatively short lifespan of millions of years, whereas lower mass stars eventually end up redder and much fainter and may live for hundreds of billions of years. The younger short-lived stars are found in the disc of the galaxy, where new stars continue to form, whereas older stars dominate in the bulge around the galactic centre and in the halo that surrounds the disc.

Some star-forming regions are found at the outer edge of the disc, and models of galaxy formation predict that the new stars will slowly increase the size of the galaxy they reside in. One problem in establishing the shape of the Milky Way is that we live inside it, so astronomers look at similar galaxies elsewhere as analogues for our own.

Martínez-Lombilla and her colleagues set out to establish whether other spiral galaxies similar to the Milky Way really are getting bigger, and if so what this means for our own galaxy. She and her team used the ground-based SDSS telescope for optical data, and the two space telescopes GALEX and Spitzer for near-UV and near-infrared data respectively, to look in detail at the colors and the motions of the stars at the end of the disc found in the other galaxies.

The researchers measured the light in these regions, predominantly originating from young blue stars, and measured their vertical movement (up and down from the disc) of the stars to work out how long it will take them to move away from their birthplaces, and how their host galaxies were growing in size.

Based on this, they calculate that galaxies like the Milky Way are growing at around 500 meters per second.
This slow growth may be moot in the distant future. The Milky Way is predicted to collide with the neighbouring Andromeda Galaxy in about 4 billion years, and the shape of both will then change radically as they merge.

The Daily Galaxy via RAS

Composition_of_ESO_observatories

"The Galaxy" in Your Inbox, Free, Daily