Astronomers spot most distant luminous galaxies

Contributed by
Aug 9, 2007
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This is very cool: astronomers have spotted extremely distant, extremely bright galaxies. The newly released observations are amazing for many reasons; let me walk you through this.

The top of the three images is from a telescope that looks at light that has a wavelength in the millimeter range, so you can think of it as very far-infrared. That huge blob is a bright source of this light, but what is it? That's a problem-- it's hard to identify what type of object it is from such a low-resolution image.

So then you look at in in the mid-infrared using the

Spitzer Space Telescope Smithsonian’s Submillimeter Array, and you get the middle image. Better! Although still a little blobby, the position of the source can be nailed down with much higher precision. But still, what is it?

Well, why not take a Hubble image? That's the bottom one. The only source at the position of the other two images is a faint little dot. By examining the way the object emits light at different wavelengths (basically thinking of these images as very low resolution spectra), the distance to the object is determined to be at least 11.5 billion light years. There is a small chance it is much closer and a different kind of object, but given its characteristics this seems unlikely.

This object is one of six found in this way. These objects are very young galaxies experiencing heavy starbirth pangs. The young stars crank out dust, which blocks the visible light, but makes them very bright in the infrared. In fact, most of the objects found this way have no visible emission detected; the one shown here is one that happens to be visible... barely. It's at a (red) magnitude of about 26, meaning that the faintest star you can see with your unaided eye is still 100,000,000 times brighter than that galaxy! That's faint.

These galaxies are called ULIRGs, for Ultra Luminous InfraRed Galaxies. They are so far away that we are seeing them as they were just 2 billion years after the Universe itself formed, which is pretty young. Models of how stars and galaxies form have a hard time getting them to be so dusty so early, which means that somewhere in these models there is something missing that the Universe is doing. What is different about the young Universe that we're not seeing? How do we improve the models so that we can fit what we see, and then test them using further observations?

One idea is that the galaxies are undergoing collisions with other galaxies. This generally triggers vast amounts of star formation, so that could explain why these guys are so madly cranking out stars. It also means that a lot of gas and dust from the collision will be funneled into these galaxies' central black holes, which in turn means that in a few million or billion years, these galaxies will turn into quasars: objects with incredibly bright central regions as the supermassive black holes there gobble down all that material.

So keep your eyes on these guys. If you can wait an eon or two, they'll get even more interesting.

Here is the scientific journal paper on these objects for those who are interested.