A new image from the NASA/ESA Hubble Space Telescope shows a distant galaxy as it begins to align with and pass behind a Sun-like star sitting nearer to us within our own Milky Way Galaxy.
The Sun-like star HD 107146 sits at the centre of this Hubble/STIS image. The position of the star is marked with a green circle. The Vermin Galaxy is visible as the smudge to the lower right. Image credit: NASA / ESA / Hubble.
The star in question, called HD 107146, is a G2V star, approximately 89 light-years away in the constellation Coma Berenices.
It has a magnitude of 7 and cannot be seen with the naked eye but is visible through a small telescope.
Its light has been blocked in this Hubble image to make its immediate surroundings visible.
The concentric orange circle surrounding HD 107146 is a circumstellar disc — a disc of debris orbiting the star.
In the case of HD 107146 we see the disc face-on.
As this star very much resembles our Sun, it is an interesting scientific target to study: HD 107146’s debris disc could be analogous to Solar System’s asteroids and its Kuiper Belt, a frigid, vast frontier of icy bodies left over from the Solar System’s construction 4.6 billion years ago.
A detailed study of the HD 107146 system is possible because of the much more distant galaxy as the star passes in front of it.
HD 107146’s circumstellar disk is already at the edge-of-transit with the galaxy, i.e. the light of the disk is contaminated by that of the galaxy, hence astronomers nicknamed it the Vermin Galaxy.
The unusual pairing was first observed in 2004 by Hubble’s Advanced Camera for Surveys (ACS) and again in 2011 by Hubble’s Space Telescope Imaging Spectrograph (STIS).
The Vermin Galaxy will not be fully obscured until around 2020, but interesting science can be done even while the galaxy is only partly obscured.
Light from the galaxy will pass through the star’s debris discs before reaching our telescopes, allowing us to study the properties of the light and how it changes, and thus infer the characteristics of the disc itself.
