S&T: A New Galactic Yardstick

[Ann]

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Astronomers have developed a new method to measure distances to bright but faraway galaxies, a tool which will help better constrain the expansion rate of the universe.

The nature of the universe lies within a single constant. Measuring this one number — known as the Hubble constant — tells us the universe’s expansion rate, its age, and ultimately, its fate. Now a team of astronomers led by Yuzuru Yoshii (University of Tokyo) has developed an entirely new method to measure this crucial number.

Yoshii and colleagues think they’ve found a new standard candle: active galactic nuclei (AGN). These supermassive black holes at the centers of distant galaxies gobble down gas at furious rates. The gas heats up and shines brightly in the process, often outshining its host galaxy.

Since AGN are 10 to 100 times brighter than Type 1a supernovae, they could probe much larger distances, marking a giant leap in the cosmic distance ladder. (OK it would still be within the nearby universe.) But AGN can be wildly different beasts — how can astronomers tame them to be standard candles?

It all comes down to dust, says coauthor Bruce Peterson (Australian National University). Dust forms around the black hole nesting at the center of a galaxy, but it can’t form too close to the heat of the black hole’s accretion disk. Instead, the dust grains can only form in a more distant ring, leaving a gap between the accretion disk and the dust ring. The size of the gap is dependent on the heat, or brightness, of the black hole's accretion disk. Measure the size of the gap, and you’ll have a measure of the AGN’s intrinsic brightness — and hence its distance.

Read more here.

Ann

[MargaritaMc]

http://asterisk.apod.com/viewtopic.php?f=31&t=33120
This thread has info about this finding, with links to the arXiv paper and an explanatory astrobite.

M