Whirlpool Awash with Hints and Promise

Sometimes, seeing is not just believing, seeing is celebrating.

Astronomers working with the Herschel mission are in good spirits this week after capturing a stunning new image of M51, the Whirlpool galaxy. The galaxy’s elegant spiral arms can easily be discerned in the infrared image, which is far sharper at long wavelengths than images by Herschel's predecessor, NASA’s Spitzer Space Telescope.

The red, green and blue colours in this image correspond to the 160, 100, and 70 µm wavelength bands of the Herschel/PACS instrument.
ESA & The PACS Consortium
“It’s very exciting to see the first images from Herschel,” says Christine Wilson of McMaster University in Hamilton, Ontario. Wilson leads the Herschel Key Project, which will characterize interstellar dust in nearby galaxies.

“M51 is one of our targets,” says Wilson. “The picture is really spectacular and I have been thinking today about what it means.”

The sharpness of the image comes as a relief to project scientists, since Herschel's optical components cannot be adjusted after launch. Because of the way the spacecraft was designed and constructed it was not possible to test all the telescope's optical components together at the same time.

Among the interesting details in the new image is the slight color difference between M51 and a smaller elliptical galaxy, which appears as a bright bluish dot in the upper left part of the image. This galaxy is passing by the Whirlpool and has been gravitationally interacting with it for millions of years. According to Wilson, the contrasting colors hint at “some difference in the emission processes in the two galaxies.”

The Herschel Key Project will focus on 13 relatively close galaxies including some that are merging or have been disrupted by past collisions. Among the questions the project seeks to answer is whether different kinds of galaxies, such ellipticals and spirals have different kinds of dust mixed in among their stars.

Herschel is ideal for measuring the size, composition and temperature of dust grains within the Milky Way and in distant galaxies. Dust naturally absorbs light from stars and re-emits that energy at infrared wavelengths. The study of dust is particularly important in astronomy because dust is crucial to the formation of solar systems with rocky planets like Earth.

With a primary mirror 3.5 meters across, Herschel became the largest space telescope ever when it was launched by the European Space Agency on May 14th. It is currently on its way to L2, a point some 1.5 million km away where the combined gravitational pull of the Sun and Earth allow spacecraft to travel in sync with our planet.

Herschel’s relatively larger mirror accounts for why its view is so much sharper at some wavelengths than Spitzer’s. You can find a comparison of the two here.

M51 is located about 25 million light-years from the Milky Way. Its grand design spiral shape and face-on orientation have made it a perennial favorite with backyard astronomers.


Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

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