This rendering shows a snapshot from a cosmological simulation of a Lyman-alpha Blob similar to LAB-1. Embedded at the center of this system are two strongly star-forming galaxies, but these are surrounded by hot gas and many smaller satellite galaxies that appear as small red clumps of gas here. J.Geach/D.Narayanan/R.Crain

Massive blobs of glowing hydrogen gas in the far reaches of the universe have puzzled astronomers ever since they were first observed in 2000. These Lyman-alpha Blobs (LABs) are among the largest known objects in the entire universe, some more than 400,000 light years across, or four times the width of the Milky Way. The enormous clouds emit large amounts of ultraviolet light with a spectral line produced by hydrogen ions, known as a Lyman-alpha line. Until now, the source of energy illuminating the gargantuan blobs has remained a mystery to astronomers.

It is now believed that the most massive galaxies in the universe form within these Lyman-alpha Blobs.

New observations with many of the most powerful telescopes in the world—including the Atacama Large Millimeter Array (ALMA) in Chile, the ESO's Very Large Telescope (VLT), and the Hubble Space Telescope—have revealed that two large galaxies engaging in furious star formation are at the center of the gigantic cloud of gas that is SSA22-Lyman-alpha Blob 1, or LAB-1. The first discovered and most thoroughly studied blob, LAB-1 sits about 11.5 billion light years away from us. The galaxies at its center are igniting new stars at a rate over 100 times that of the Milky Way, brightly illuminating the colossal blob of hydrogen gas surrounding them. The new research was published today in the Astrophysical Journal.

This diagram explains how a Lyman-alpha Blob, one of the largest and brightest objects in the Universe, shines. ESO/J. Geach

In addition to the two primary galaxies, which are destined to merge into one even larger elliptical galaxy, there appears to be a host of smaller galaxies swarming around Lyman-alpha Blob 1, possibly bombarding the bigger galaxies with material to drive the high rate of star formation. Astronomers now believe that LAB-1 is an early stage in the formation of a massive cluster of galaxies, similar to clusters we see closer to the Milky Way.

It is important to remember that observing an object 11.5 billion light years away means that we are seeing what it looked like 11.5 billion years ago—a mere 2.3 billion years after the Big Bang. LAB-1 is an ancient artifact of the early universe, and studying it with other Lyman-alpha Blobs can help astronomers refine theories about galactic formation, the fabric of space-time, and the structure of the universe itself. It is now believed that the most massive galaxies in the universe form within these Lyman-alpha Blobs.

"What's exciting about these blobs is that we are getting a rare glimpse of what's happening around these young, growing galaxies," said Jim Geach, an astrophysicist from the University of Hertfordshire, U.K., who led the international research team. "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."

Source: National Radio Astronomy Observatory

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