The Earliest Stars?
Posted by John Baez
You may have read about this in the news, but here are the original articles:
- A. Kashlinsky, R. G. Arendt, J. Mather and S. H. Moseley, New measurements of cosmic infrared background fluctuations from early epochs, to appear in Ap. J. Letters.
- A. Kashlinsky, R. G. Arendt, J. Mather and S. H. Moseley, On the nature of the sources of the cosmic infrared background, to appear in Ap. J. Letters.
Executive summary: using delicate techniques to carefully sift through the infrared background radiation, the authors claim to find radiation not accounted for by previously known sources. Assuming the now-standard ΛCDM cosmology, the sources of this radiation date back to less than 1 billion years after the Big Bang, and were individually much brighter than current-day stars.
Here’s a picture of the data:
On top is a photograph taken by the Spitzer Space Telescope: a 10-hour infrared exposure of a tiny patch of sky, 6 × 12 arcminutes across, chosen for having a bare minimum of foreground stars, galaxies and dust. (For comparison, the Moon is 30 arcminutes across.) On the bottom is the same picture with known sources of infrared subtracted. What’s left may be the severely redshifted light from early stars!
Or, it may not. Ned Wright of UCLA has said “I’m very skeptical of this result. I think it’s wrong. I think what they’re seeing is incompletely subtracted residuals from nearby sources.”
The first stars play an interesting role in the history of the Universe. Roughly 380,000 years after the Big Bang, the hot hydrogen and helium forming our Universe cooled down to 3000 kelvin — cool enough to no longer be ionized, so light could freely pass through. The period from then until the first stars formed is called the “Dark Ages”. During this era, gas cooled down and clumped under its own gravity — perhaps with a lot of help from dark matter.
In keeping with their name, the Dark Ages are still shrouded in mystery. Which formed first — stars or galaxies? And, when did the Dark Ages end? It’s currently believed that the first stars formed sometime between 150 million and 1 billion years after the Big Bang. At the later end of that range, the Universe could have gotten quite cold before starlight warmed up the interstellar gas and reionized it.
There’s even a spooky theory that the Universe was full of hydrogen snowflakes near the end of the Dark Ages. But, the current best guess, based on WMAP data, says that reionization happened 400 million years after the Big Bang. This would too early for hydrogen snow, since my rough calculation says the microwave background radiation was 30 kelvin then, while hydrogen freezes at 14 kelvin.
The first stars are believed to have been very large: perhaps hundreds of times the size of our Sun! But, these so-called “Population III” stars have not actually been seen — hence the fuss surrounding Kashlinsky et al’s paper. When these stars died and exploded, they began the first stage of a process, still underway, in which the interstellar gas of the Universe became ever more rich in heavier elements.
The Universe is a fascinating place. Merry Christmas!
Re: The Earliest Stars?
Speaking of the Dark Ages — I have a little timeline of the history of the universe, and it has an embarrassingly large gap between 13.3 billion years ago (“reionization” - when the first stars heated and reionized the hydrogen gas forming most of our universe at the time) and 4.55 billion years ago (the formation of the Sun).
Does anyone know some dates of exciting events between these two times? I can’t believe it was a completely boring stretch…
The formation of the Milky Way?
The first galaxies?
The first supernovae?
The first quasars?
The first population II stars?
The first population I stars?
Other stuff?
(By the way, I don’t actually believe we know the two dates listed above as accurately as I’ve quoted them! People use these figures, but I wouldn’t be surprised if the last one or two decimals change in the future.)