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This galaxy, Messier 90, appears blue because it’s traveling toward us

Messier 90, a beautiful spiral galaxy located roughly 60 million light-years from the Milky Way in the constellation of Virgo (The Virgin). The black boxes in the top left are the result of the configuration of the sensors in the camera. ESA/Hubble & NASA, W. Sargent et al.

A new Hubble image has been released showing Messier 90, 60 million light-years away in the Virgo Cluster. It is located in the constellation of Virgo (The Virgin), which is part of the Virgo Supercluster which includes our galaxy.

An unusual feature of Messier 90 is that it is traveling towards the Milky Way, not away from it. Most galaxies are traveling apart due to the expansion of the universe, so other galaxies appear to be moving away from us. But Messier 90 is heading in our direction; a rare example of bucking the galactic trend.

We know that Messier 90 is traveling towards us because of the way its light appears. When galaxies are traveling away from us, the wavelengths of light they produce is stretched, making the light appear more towards the red end of the spectrum in a process called the Doppler effect. This means most galaxies give off light which is redshifted. But in the case of Messier 90, the light we detect from it is shifted towards the blue end of the spectrum, or blueshifted. That means light waves are being compressed as the galaxy comes closer to us.

Astronomers believe the galaxy is currently traveling towards us due to the huge mass of the Virgo Cluster, which pulls smaller galaxies into eccentric orbits which travel sometimes closer to us and sometimes further away.

This image of Messier 90 was created from a wide range of light wavelengths, including infrared, ultraviolet, and visible light. The data was gathered by Hubble’s Wide Field and Planetary Camera 2 (WFPC2) which captured images from Hubble between 1994 and 2010.

The reason this image has a black section in the top left corner is to do with how the WFPC2 worked. The camera consisted of four light detectors, each trained on a slightly different area of space with some small overlap between them. There were three wide-field sensors in an L-shape and a smaller, higher resolution sensor in the remaining corner. As the higher resolution camera captured images at a greater magnification, the image it produced had to be scaled down in order to fit with the other three images. The result is images like the one above, with a chunk missing from the top corner.

The WFPC2 has since been superseded by the Wide Field Camera 3 (WFC3) which captures full images over a wide range of wavelengths.

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