An international team of astronomers led by the UK’s University of Hertfordshire have solved the mysteries of a giant space blob by witnessing galaxies forming inside the intergalactic gas cloud.
Lyman-alpha Blobs (LABs) are gigantic clouds of hydrogen gas that can span hundreds of thousands of light years and glow far more brightly than scientists expect. And since their discovery, the processes that makes LABs glow so intensely has been an astronomical puzzle, until now. Scientists, led by Dr James Geach from the University’s Centre for Astrophysics Research, have confirmed that young galaxies are forming within the blobs, causing them to glow.
One of the largest LABs known, is SSA22-Lyman-alpha blob 1, also simply known as LAB-1. Within LAB-1 the team of scientists have found that two galaxies are forming and the blob is actually creating stars at a rate 100 times faster than our own galaxy, the Milky Way. It this intense nature of star formation that is lighting up the gas cloud so brightly.
Lead author Dr Geach explained: “Think of a streetlight on a foggy night — you see the diffuse glow because light is scattering off the tiny water droplets. A similar thing is happening here, except the streetlight is an intensely star-forming galaxy and the fog is a huge cloud of intergalactic gas. The galaxies are illuminating their surroundings.”
LAB-1 is the very first object of its kind discovered and was found 15 years ago. It is located so far away that its light has taken approximately 11.5 billion years to reach Earth. It measures 300,000 light years across and is three times larger than the Milky Way.
To monitor such a large mass, the international team, led by the University of Hertfordshire, used the Atacama Large Millimeter/Submillimeter Array (ALMA), a group of highly developed telescopes that can observe light from dust clouds in distant galaxies millions of light years away.
This meant they could accurately pinpoint several sources of radiation and light within the space blob, where they spotted the two young, growing elliptical galaxies. They then combined the ALMA images with observations from the Multi Unit Spectroscopic Explorer (MUSE) instrument mounted on European Southern Observatory’s Very Large Telescope (VLT). This maps the light that is emitted from the blob, known as Lyman-alpha light and it showed that the sources of light are the forming stars in the very heart of the Lyman-alpha Blob.
Then deep imaging with the NASA/ESA Hubble Space Telescope and spectroscopy at the W. M. Keck Observatory showed in addition that the ALMA sources are surrounded by numerous faint companion galaxies that could be bombarding the central ALMA sources with material, helping to drive their high star formation rates.
Dr Geach added: "What’s exciting about these blobs is that we are getting a rare glimpse of what’s happening around these young, growing galaxies. For a long time the origin of the extended Lyman-alpha light has been controversial. But with the combination of new observations and cutting-edge simulations, we think we have solved a 15-year-old mystery: Lyman-alpha Blob-1 is the site of formation of a massive elliptical galaxy that will one day be the heart of a giant cluster. We are seeing a snapshot of the assembly of that galaxy 11.5 billion years ago."
