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Thursday, 23 April 2009 18:40

Himiko blob found: Earliest known beginning of galaxy

Astronomers have discovered a massive object about 12.9 billion light-years from our Solar System that is the earliest known precursor to a galaxy. It appears to have first formed during the early times of our Universe—less than one billion years after the Big Bang explosion.

This massive and mysterious gas blob is in a shape that represents the early beginning of a galaxy. It has been called Himiko, after an ancient and equally mysterious Japanese queen.

Even though discovered, it still remains mostly a mysterious object to astronomers as they scramble to learn more about it.

According to the April 23, 2009 Space.com article “Giant Mystery Blob Discovered Near Dawn of Time,” the announcement of this important discovery for cosmologists was made on Wednesday, April 22, 2009, by the U.S., British, and Japanese team led by Masami Ouchi, a U.S. researcher at the Carnegie Institution of Washington, in Pasadena, California.

Dr. Ouchi states, "I have never imagined that such a large object could exist at this early stage of the universe's history.” [AFP: “Colossal new space oddity Himiko baffles scientists”]

The result of the discovery of the Himiko blob was published in the article “Discovery Of A Giant Lyα Emitter Near The Reionization Epoch,” within the May 2009 issue of The Astrophysical Journal (ApJ 696 1164-1175 doi: 10.1088/0004-637X/696/2/1164).

The massive, gas blob is thought to have formed about 800 million years after the explosion of the Big Bang, which is theorized to have started our Universe about 13.7 billion years ago. Thus, it would have formed about 12.9 billion years ago.

The Ouchi team are fortunate just to have discovered the Himiko blog because of its extreme distance from Earth. They used 2007 data from a Spitzer/Infrared Array Camera (IRAC) while using the Subaru Telescope as part of the Subaru/XMM-Newton Deep Survey (SXNDS).

Page two continues.

They followed up this survey with observations from the Keck/DEIMOS and Magellan/IMACS arrays. These instruments identified ionized hydrogen gas within the light (radiation) that was emitted from Himiko and impinged on the telescopes 12.9 billion years later.

An image, taken by the Ouchi team, of the Himiko blog, the most massive object discovered so far in the early Universe, is found within the Carnegie Institution for Science web page called “Himiko.”

Dr. Ouchi stated, "I have never heard about any [similar] objects that could be resolved at this distance. It's kind of record-breaking." [Space.com]

Astronomers have already discovered similar blobs, called Lyman-Alpha blobs, which were formed two to three billion years after the Big Bang explosion. However, this blob formed much earlier than these LABs, which makes it very special to astronomers.

The Himiko is about ten times more massive than the largest of these Lyman-Alpha blobs. The mass of Himiko is equivalent to the mass of about 40 billion stars about the same size as our Sun.

Himiko is also about 55,000 light-years across (that is, it takes light (radiation) about 55,000 light-years to across it). Compared to our Milky Way Galaxy, it is about one-half its diameter.

The time that Himiko formed is called by cosmologists as the Reionization Epoch because hot, energetic hydrogen gas was just beginning to come together to form stars, and then galaxies, which created radiation (light) that astronomers now are also to observe through their huge light-gathering telescopes. The reionization epoch lasted from 0.2 to 1 billion years after the Big Bang explosion.

Page three concludes.

Dr. Ouchi and other astronomers are trying to understand more about this epoch of time. He states, “Even for astronomers, we don't understand. We are keen to try to understand what those systems are in the reionization epoch."

Space.com states, “Himiko may represent an ionized gas halo surrounding a super-massive black hole, or a cooling gas cloud that indicates a primordial galaxy, Ouchi noted. But it might also be the result of a collision between two young galaxies, or the outgoing wind of a highly active star nursery, or a single giant galaxy.”

They conclude in their abstract, “Although the nature of this object is not yet clearly understood, this could be an important object for studying cooling clouds accreting onto a massive halo, or forming-massive galaxies with significant outflows contributing to cosmic reionization and metal enrichment of intergalactic medium.”

Dr. James Dunlop, one of the team members, stated, “Using infrared data from NASA’s Spitzer Space Telescope and the United Kingdom Infrared Telescope, radio data from the VLA, and X-ray imaging from the XMM-Newton satellite, we were able to estimate the star-formation rate and stellar mass of this galaxy and to investigate whether it contains an active nucleus powered by a super-massive black hole."

And, "We found that the stellar mass of Himiko is an order of magnitude larger than other objects known at a similar epoch, but we cannot as yet tell if the center houses an active and growing black hole.” [Carnegie Institution for Science (CIS): “Mysterious Space Blob Discovered at Cosmic Dawn”]

Dr. Alan Dressler, another one of the team members, stated, “One of the puzzling things about Himiko is that it is so exceptional. If this was the discovery of a class of objects that are ancestors of today’s galaxies, there should be many more smaller ones already found—a continuous distribution. Because this object is, to this point, one-of-a-kind, it makes it very hard to fit it into the prevailing model of how normal galaxies were assembled."

And, "On the other hand, that’s what makes it interesting!” [CIS]


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