Pinwheel in the Stars

Credit: NASA, ESA, A. Riess (STScI/JHU), L. Macri (Texas A&M University), and the Hubble Heritage Team (STScI/AURA)

A pinwheel of stars spins in the stellar void in this image from the NASA/ESA Hubble Space Telescope .

Explore the spiral galaxy known as NGC 5584 from the compact compact core criss-crossed with filaments of dark dust, and across the sweeping expanse of its spiral arms. The core’s golden light comes from middle-aged yellow stars like our Sun. You can follow those yellow stars outward along the spiral arms. Tracing along the leading edges of the spiral arms, blue patches of starlight show areas of new star formation. As the spiral arms sweep around the galactic center, gas and dust are pushed together. Over time, gravity makes the dense pockets of gas and dust tighter making a perfect place for stars to begin to glow. Look for many reddish and faraway background galaxies in the image. How many can you count?

This image is not only beautiful but is important for science too. Astronomers use images like this one to help measure the universe’s expansion rate. NGC 5584 contains a special pulsating stars called Cepheid variables. They are used by scientists as reliable distance markers because they pulse at a rate matched closely by their intrinsic brightness. Intrinsic brightness is a measure of how bright a star is at a common distance without interfering dust clouds. Scientists are interested in these measurements because they are trying to explain why universe appears to be expanding at an ever-increasing rate. Some theories for an expanding universe involve mysterious and unseen dark matter permeating the universe.

NGC 5584 lies about 72 million light-years away toward the constellation Virgo, the Maiden.

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The ancient peoples saw pictures in the sky. From those patterns in the heavens, ancient storytellers created legends about heroes, maidens, dragons, bears, centaurs, dogs and mythical creatures...
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