Whirlpool Galaxy
What is Whirlpool Galaxy?
Galaxies· Distance ~23 million ly. A spiral galaxy in Canes Venatici whose two bold arms, seen face-on, look like a textbook drawing. A small companion galaxy sits at the end of one arm. In 1845 Lord Rosse saw its spiral shape, the first time a spiral was noticed in any such object.
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Its place in the sky
A galaxy, in the direction of Canes Venatici, spanning about 11 arcminutes of sky — 0.4 times the width of the full Moon.
Distance and scale
| Distance | ~23 million ly |
|---|---|
| Diameter | ~76,000 ly |
| Companion | NGC 5195, hanging off one arm |
| Constellation | Canes Venatici |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Discovery and name
In 1845 Lord Rosse sketched its arms with his giant "Leviathan" — the first spiral structure ever seen.
Three supernovae in seventeen years in the Whirlpool
Supernovae went off in the Whirlpool in 1994, 2005 and 2011, three in seventeen years. A galaxy the size of the Milky Way is usually expected to have one or two a century, so this is a lot. The passing companion NGC 5195 stirred up the gas and set off the birth of many heavy stars. Heavy stars live short lives and explode early, which is thought to explain the high rate.
For the 2011 supernova, SN 2011dh, Hubble had already photographed the spot before the explosion. This let astronomers look back and see which star had blown up. It was a yellowish supergiant. Supernovae were thought to come mostly from red or blue supergiants, so the result was a surprise. The supernova reached about magnitude 12, bright enough for a small telescope.
The galaxy in depth
The Whirlpool Galaxy is number 51 in Messier's list, so it is also called M51. It lies about 23 million light-years away in Canes Venatici. It is about 76,000 light-years across, a little smaller than the Milky Way. Its disc faces us directly, so two thick spiral arms stand out clearly. That is why it is often used as the standard example of a spiral galaxy.
A small galaxy, NGC 5195, sits at the end of one arm. Over hundreds of millions of years it has passed close to the Whirlpool and tugged on it with its gravity. Scientists think this is why the spiral arms are so sharp. Regions where new stars are forming line the arms like beads, making it a good place to study how spiral arms create stars.
In 1845 Lord Rosse in Ireland looked at it through a large reflecting telescope 1.8 m wide and sketched its spiral shape. Nobody knew then that it was a galaxy, but it was the first time a spiral structure had been seen. To find it, start at Alkaid, the star at the end of the Big Dipper's handle, and move a little to the south-west. From a dark site, binoculars show the two galaxy centres side by side as faint smudges.
Frequently asked
- How far is Whirlpool Galaxy from Earth?
- The distance of Whirlpool Galaxy is ~23 million ly.
- How big is Whirlpool Galaxy?
- The diameter of Whirlpool Galaxy is ~76,000 ly.
- Where in the sky is Whirlpool Galaxy?
- Whirlpool Galaxy lies in the direction of Canes Venatici.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.