Hubble鈥檚 Ultra Deep Field just got even deeper. Astronomers have found 72 mysterious new galaxies in this tiny spot of the sky that were too faint for even the Hubble space telescope to see.
The Hubble Ultra Deep Field is an image of a small region of relatively dark space next to the Fornax constellation. Though the image only covers an extremely small fraction of the sky, it contains about 10,000 galaxies.
Now, astronomers using the Multi Unit Spectroscopic Explorer (MUSE) instrument on ESO鈥檚 Very Large Telescope in Chile have looked even deeper into the same region and examined the light from 1600 faint galaxies, including 72 that we had never seen before.
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鈥淭hese galaxies are not unexpected, but nobody thought we would see them,鈥� says at the University of Leiden in the Netherlands. 鈥淲e thought that Hubble would have been able to see all the galaxies that were there.鈥�
Zooming in
Generally, we detect galaxies by looking for their bright stars. But the light from nearby bright stars can drown out dimmer galaxies like the 72 new ones, all of which contain stars too dim for Hubble to see.
鈥淚t鈥檚 like if you鈥檙e surrounded by lots of noisy family members and someone鈥檚 playing a very quiet musical instrument and you want to just hear the musical instrument. With MUSE, you can really zoom in on that one wavelength,鈥� Brinchmann says.
The new galaxies all shine at one particular wavelength of light, known as Lyman-alpha emission, which comes from the glow of hydrogen gas. Because MUSE works by dividing light up into wavelengths, it was able to detect a spike in the light of that wavelength which would have otherwise remained invisible.
No stars in sight
Astronomers are not quite sure why these galaxies seem to shine in only one colour, revealing the hydrogen but no stars. We know the stars ought to be there, because these Lyman-alpha emissions are a result of hydrogen ionised by stars.
鈥淎 galaxy is not a closed system, so this is really essential to understanding how gas comes into or goes out of galaxies,鈥� says Brinchmann. These tiny galaxies are the building blocks for the behemoths we see today, so their glowing hydrogen halos could help us understand how modern galaxies came to be.
Astronomy & Astrophysics
Read more: We鈥檝e found a bunch of dwarf galaxies we thought didn鈥檛 exist
