This giant blob of hydrogen gas may hide a distant galaxy, one of the earliest yet found (Image: M Ouichi et al)

Astronomers have spotted the most distant blob of gas ever seen and are puzzling over what it is. It dates from the very early universe, and its large size may pose a challenge to prevailing models, which state that massive objects tend to grow up slowly over time via mergers.

The gas cloud – which may conceal a galaxy – is known as a Lyman-alpha blob, named for a particular wavelength of light released when an electron loses energy in a hydrogen atom.

It spans some 55,000 light years, about half the width of the Milky Way, and it sits some 12.9 billion light years from Earth. That means we are seeing it as it was 12.9 billion years ago, when the universe was just 800 million years old. It is the most distant Lyman-alpha blob ever seen and the fourth most distant object yet spotted.


Masami Ouchi of the Observatories of the Carnegie Institution in Pasadena, California, and colleagues first spotted the gas in images of the deep sky taken with the Subaru Telescope on Mauna Kea in Hawaii.

The exact nature of the object is not known. It could be a galaxy lit either by a ravenous supermassive black hole at its centre or by the heat of an intense burst of star formation. But it could also be two merging galaxies, or a developing galaxy that is gobbling up a large amount of gas.

Massive find

What is clear is its massive size. The object weighs an estimated 40 billion times the mass of the sun, making it some 10 times more massive than other galaxies that have been found at that time, Ouchi told New Scientist.

Finding such a large galaxy early on – when the universe’s first stars and galaxies were forming – could challenge the prevailing model of galaxy formation, in which massive galaxies grow slowly from successive mergers with smaller galaxies. The discovery may hint that “standard galaxy formation models may be wrong or may need some corrections”, Ouchi says.

But Avi Loeb of the Harvard-Smithsonian Center for Astrophysics says one mammoth galaxy is not an immediate problem, since models allow for a few to form soon after the big bang, in relatively large cradles of dark matter. “The standard model predicts the existence of such systems early on at the appropriate abundance,” Loeb told New Scientist.

The team hopes future X-ray images will reveal whether the object is lit by a supermassive black hole that is devouring its surroundings, a process that emits X-rays.

Higher-resolution pictures could also discern whether the object is actually a pair of merging galaxies. This might be accomplished with the Hubble Space Telescope’s new Wide Field Camera 3, which is set to be installed in May (see Pimp my scope: Revamping Hubble).

Journal reference: The Astrophysical Journal (v 696, p 1164)