Tag: NGC 5584

The Universe is expanding at 73.8 +/- 2.4 km/sec/megaparsec! So there.

By Phil Plait | March 22, 2011 7:00 am

In 1998, two teams of astronomers independently reported amazing and bizarre news: the Universal expansion known for decades was not slowing down as expected, but was speeding up. Something was accelerating the Universe.

Since then, the existence of this something was fiercely debated, but time after time it fought with and overcame objections. Almost all professional astronomers now accept it’s real, but we still don’t know what the heck is causing it. So scientists keep going back to the telescopes and try to figure it out.

[Click to galactinate, or grab the cosmic 3500 x 4000 pixel browser bruiser.]

This gorgeous image is of the nearby spiral galaxy NGC 5584, where of course "nearby" to an astronomer means 72 million light years. This galaxy is loaded with a specific type of variable star — called Cepheids — which are very important: the way they change their brightness depends on how luminous they are. Measure the change, and you measure the luminosity, and if you measure how bright they appear in the sky you get their distance. It’s a bit like judging how far away a car is by gauging how bright its headlights are. Except in this case astronomers use Hubble instead of their eyes. It’s a tad more accurate.

It so happens that in 2007, NGC 5584 was the host of a Type Ia supernova, the Golden Standard of distance indicators. These are so bright they can be seen clear across the Universe! By knowing the distance to the one in NGC 5584, we can then use that to get the distances to supernovae much, much farther away.

It’s a bootstrappy way of measuring the cosmic distance scale.

But it appears to work. Read More

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