An extragalactic star-forming region
This video shows a view of M33, also known as the Triangulum galaxy, taken by ESA's Gaia satellite, zooming in to show the star-forming region NGC 604, first as viewed by Gaia and then by the NASA/ESA Hubble Space Telescope.
Located some 2.4 million light-years away, M33 is one of our neighbouring galaxies and is part of the Local Group, the assembly of galaxies that includes our Milky Way and the Andromeda galaxy. A spiral galaxy with less than one tenth the mass of the Milky Way or Andromeda, M33 is the third largest member of the Local Group and is thought to be a satellite galaxy of Andromeda.
Gaia's detections correspond to about 40 000 of the galaxy's brightest stars, a small fraction of the total stellar population of M33, which amounts to roughly 40 billion stars.
A red square indicates the star-forming region NGC 604, which is located to the top left of M33's centre in this view.
The video zooms in to show Gaia's view of NGC 604, and finally fades to reveal Hubble's image
The comparison between the Gaia and Hubble views shows that Gaia has detected about 150 individual stars in the NGC 604 region, which spans only about 0.55 square arcminutes in the sky. This number might not sound big in absolute terms, but it is impressive when considering that the observed field is about 2000 times smaller than the area covered by the full Moon in the sky, revealing that Gaia is able to detect a significant number of extragalactic stars.
This is even more remarkable given that Gaia's observed stars are automatic detections obtained by the satellite's onboard computing system while scanning over the region, whereas the stars detected in astronomical images, such as those from Hubble, are the result of dedicated observations obtained by pointing at specific regions on the sky, which are later analysed by scientists.