Messier 90: Spiral Galaxy in Virgo

M90 is one of the largest spiral galaxies in the Virgo Cluster, and one of the few that is moving toward us rather than away. It sits just north of M89, and the two make a nice contrast in one low-power field.

What it is

M90 is a spiral galaxy about 59 million light-years away. Its visible disk spans well over 100,000 light-years, and we see it tilted steeply, so it looks like a long oval. Most galaxies recede from us as the universe expands, but M90 has a blueshift: like M86, it is moving through the cluster toward us fast enough to overcome that expansion.

M90 is a good example of what a crowded cluster does to a spiral. As it moves through the Virgo Cluster's hot gas, much of the gas in its outer disk has been stripped away. Its outer arms look smooth and featureless, with few young stars, while star formation carries on only near the center. Astronomers sometimes call galaxies like this "anemic" spirals.

When to see it

From about 40°N, M90 is highest around midnight in early April and around 10 p.m. standard time (11 p.m. daylight time) in early May, reaching about 63° above the southern horizon. It is visible from most of the Southern Hemisphere too, in the northern sky in autumn.

How to find it

Begin at M84 and M86, which lie at the midpoint of the line from Denebola, the star at Leo's tail, to Vindemiatrix (Epsilon Virginis). Go about 1.5° southeast to M87, then about 1.2° east to M89. M90 is about 40′ north of M89. From M90, M91 lies about 1.4° to the north and M88 about 1.7° to the northwest.

What you will see

M90 is beyond most binoculars except as a faint hint under a very dark sky. In a 70–100 mm telescope it is a dim, elongated glow with a brighter middle, running roughly north-northeast to south-southwest; from the suburbs it is a challenge. A 200 mm telescope under dark skies shows a long oval with a bright, compact core and a faint, even outer disk, and dark lanes may show on good nights in larger scopes. Filters do not help.

History

Charles Messier discovered M90 on March 18, 1781, during the same night's work that added M84 through M91 to his catalog. Its blueshift was found when astronomers began measuring galaxy velocities in the 20th century, and its stripped outer disk was studied later with radio and space telescopes.