Is the Milky Way Getting Bigger?

The galaxy we inhabit, the Milky Way, may be getting even bigger, according to Cristina Martínez-Lombilla, a PhD candidate at the Instituto de Astrofísica de Canarias in Tenerife, Spain, and her collaborators. She  ]presented the work of her team in a talk on Tuesday 3 April at the European Week of Astronomy and Space Science in Liverpool.

The Solar System is located in one of the arms in the disc of a barred spiral galaxy we call the Milky Way, with a diameter of about 100,000 light years. 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 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.

NGC 4565, a spiral galaxy estimated to be 30-50 million light years away.

Credit: Ken Crawford

This is a composite image of NGC 4565 used in the new study.