First light, confirmed?

Contributed by
Jul 2, 2007

Hmph. I sometimes draft up blog entries, only to have them get buried under other drafts. I originally wrote this a few months ago, but I think it's still relevant, and it makes a point about science.

Way back in November 2005, I wrote about a Spitzer Space Telescope observation that purportedly showed light from the very first objects in the Universe.

The images were made by taking very deep exposures, then subtracting away all known light sources. What was left was a softly glowing web of light from no known source. The astronomers on the Spitzer team then said this could be the light from the very first stars. These stars were extremely massive, a hundred or more times the mass of the Sun -- and up until now have been entirely theoretical.

Well, NASA has issued a press release saying the observations have been confirmed. The press release was sparse on details. It did say that the same technique has been expanded from one to five different sections of the sky, and had been done at different wavelengths, and the results still held up. That was nice, but most of the release was the same as the one a year ago!

So I called my friend who is the PR person for Spitzer, and she told me that while the results were not yet in the journals, they were online at astro-ph, a clearing house for astronomy papers. I read the papers (here is the observation paper, and here is the results paper), and feel a bit better now. The papers are brief, but do indicate the authors did due diligence, checking through their data as carefully as possible, making sure the light they were seeing wasn't something just inside their telescope or detector. They were also able to use some simple arguments to eliminate sources like solar system objects, nearby galaxies and even relatively distant galaxies. All that's left, they claim, are the putative First Objects.

While I do think the images show something real, I'm not convinced they are from the first stars just yet. Just because you have eliminated everything you know about except for one thing, that doesn't mean that last thing must be what you see. There may be something unknown out there causing this. It's maybe not terribly likely, but it's possible. And the alternative, that they are seeing the accumulated light of thousands, millions, of first generation stars is, well, an extraordinary claim. Not a goofy one, or a crazy one -- they may very well be right! -- but a big enough claim that I'd like to see some independent confirmation.

I don't think that will come until the James Webb Space Telescope is launched, sometime in the distant future (like 2013, according to the NASA site about it). These observations have to be done in the infrared (the light from these objects is heavily shifted to that wavelength) and no other 'scope can go as deep as Spitzer right now. Unless someone thinks of a different and clever way to do this, the confirmation of these results will simply have to wait.

... although, hmmmm. When one of these stars blows up, it should make a gamma-ray burst, an intense flash of high-energy light. If one were to explode, and it were caught by the Swift satellite, then maybe we might have more evidence of these objects. Swift might do it; we've had a couple of bursts that for a while looked good (but turned out to be much closer than the oldest stars). It's too much to ask that a burst appear right on top of the light Spitzer saw: the area of sky Spitzer looked at was tiny, so the odds are extremely low. But a burst with a confirmed redshift putting it at the right distance would be interesting indeed.

Science is a tough road to walk on, and sometimes the big discoveries are first just barely seen when pushing your machines to the limits. Maybe these observations will pan out, and maybe they won't. But either way, I'm pretty sure we'll learn something important.

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