Whirlpool Galaxy

Basic Information

What is this?

The Whirlpool Galaxy

Where is it in the sky?

In the constellation of Canes Venatici, the Hunting Dogs

How big is it?

It has the mass of 160 billion Suns, or around a quarter to a third of the mass of our own Galaxy

How far away is it?

About 23 million light years, in the "M51 group" of galaxies

What do the colours represent?

Red is cooler light; blue is warmer light

Shortly after removing the protective cover from its cryostat, the PACS instrument snapped this image of the Whirlpook Galaxy.  All three channels of the instrument, 70, 100 and 160 microns, are shown as red, green and blue respectively.  The spiral arms are clearly visible, but what is shown here is not the stars but the dust which is heated up by the stars.  The bright blue blobs are warmer regions which are being heated up by stars forming within.

The bright blue region seen above the main part of the Galaxy in this image is a smaller galaxy with which M51 is in the process of merging.  Herschel observations of similar spiral galaxies will shed light on the way these galaxies have formed and the way they are forming stars at the moment.

The Whirlpool Galaxy, also known as "Messier 51" (or just M51 for short), was first catalogued in 1773 by Charles Messier.  However it was not identified as a spiral galaxy until 1845 by Earl of Rosse using a the Leviathan telescope at Birr Castle in Ireland.  At the time, this 1.82m (72") diameter telescope was the largest in the world, so it is appropriate that it is now being imaged by Herschel, the largest ever infrared telescope.

The images of the Whirlpool Galaxy in the three separate wavelength measured by PACS can be seen below.

Whirlpool Galaxy as seen in all three PACS channels


Detailed Information

Object Name: 
M51, the Whirlpool Galaxy
Type of Object: 
Spiral Galaxy
Image Scale: 
The galaxy is around 40,000 light years across
Right Ascension: 13h 29′ 52.37″ ; Declination: +47° 11′ 40.80″
Canes Venatici
Observation Date/Time: 
Sun, 14/06/2009 (All day)
70, 100, 170 microns
Distance of Object: 
23 million light years
Date of Release: