Confusing discovery: This image of the Himiko object is a composite and in false color. The thick horizontal bar at the lower right corner presents the scale of 10,000 light-years.
Credit: M. Ouchi et al
BRISBANE: Astronomers are puzzled by the discovery a giant blob of gas that existed when the universe was an infant, at just 800 million years old.
The "space blob", named Himiko after a legendary Japanese queen, is 55,000 light-years across and has a mass ten times greater than any other object discovered in the early universe, says a study to be published in The Astrophysical Journal.
Gas clouds like this can be the precursors of galaxies, and the size is comparable to the radius of the disc of our own Milky Way Galaxy.
"Never imagined"
The authors were surprised to find such a large blob at such an early stage of the universe, though, because existing theories of what followed the Big Bang suggest that small objects formed first, slowly clumping and merging over time.
"I never imagined that such a large object could exist at this early stage of the universe's history," said Masami Ouchi, the study's lead author. "This large size indicates that the physical origins of this object are different from the other ordinary galaxies that we know at this epoch."
Extended blobs like Himiko have been seen before, but most date from a time when the universe was two to three billion years old, said Ouchi, an astronomer at the Carnegie Institute of Washington in Pasadena, California. Today the universe is around 13.7 billion years old.
Himiko was found to exist in the so-called 'reionisation' epoch of the early universe, when stars, galaxies and quasars first began to form. This is as far back as astronomers can currently see, by looking at the most distant possible objects. As these objects are so far away it has taken nearly the entire history of the universe for their light to reach us.
Too far to tell
Astronomers have now observed Himiko through eight telescopes, but it is so far away that they can't really tell what it is or how it formed, Ouchi said. The blob may be ionised gas powered by a supermassive black hole, a primordial galaxy, a collision of two young galaxies, wind from intensive star formation, or a single giant galaxy, the experts said.
The next step is testing some of these possibilities with various telescopes.
The Keck Observatory's near infrared telescope in Hawaii may reveal if stars are forming within the blob, and imaging from the Chandra X-ray Observatory could show if Himiko has a supermassive black hole. The team will also use a near-infrared camera on the Hubble Space Telescope to take high-resolution images, which may tell if Himiko is the result of a galaxy merger.
Karl Glazebrook, an astrophysicist at Swinburne University in Melbourne, Australia, said it was hard to tell what the significance of the discovery would be, because so little was yet known about space blobs in general. "They're all a bit of a mystery," he added.
