M106 (NGC 4258) — Sbc in Canes Venatici

About M106 (NGC 4258)

Messier 106 is one of the best-studied spiral galaxies in the northern sky. Beyond its two bright spiral arms, radio and X-ray images show two fainter 'anomalous arms' that do not follow the stars at all: gas heated, it is thought, by material thrown out from the black hole at its centre. That central black hole is weighed unusually precisely, because water masers orbiting it act as natural radio beacons, and the same masers made M106 one of the anchors astronomers use to calibrate the distance scale of the universe.

What you are looking at

M106 is a spiral of the same broad class astronomers give the Milky Way: a moderate bulge and clearly drawn arms. Its disc is steeply tilted, about 68° from face-on, so it appears as a long oval. From edge to edge its visible disc spans about 108,000 light-years (taking its redshift distance, which for a galaxy this near is approximate), close to the width of the Milky Way.

What astronomers have recorded

SIMBAD, the reference database astronomers use, classes it as a Seyfert galaxy: its nucleus is lit by gas falling into its central black hole, though dust hides part of that glow from us. Boris Vorontsov-Velyaminov listed it as VV 448 in his catalogue of interacting galaxies. Two supernovae have been recorded in it, the first in 1981; the most recent include SN 1981K, SN 2014bc. It is cited in 2,550 scientific papers indexed by SIMBAD, and recorded there under 52 different catalogue designations.

When this light set out

The light that reaches us from M106 today set out about 22 million years ago, when grasslands were spreading across the continents. The galaxy is moving away from us at about 454 km/s (1.0 million mph), carried by the expansion of the universe. For a galaxy this close, its own motion through space is a large share of that speed, so the distance worked out from it is approximate; distances measured from individual stars in it can differ.

Finding it in the sky

M106 lies in Canes Venatici. It is best placed on spring evenings: around 9:30 pm in May it stands about 83° high in the north, close to overhead, seen from the middle of the United States.

Its neighbours

At almost the same distance from us, and so its neighbours in space as well as on the sky: NGC 4248 (0.2° away on the sky, at least 80,000 light-years from it); NGC 4346 (0.8° away on the sky, at least 320,000 light-years from it); NGC 4218 (1.0° away on the sky, at least 380,000 light-years from it); NGC 4288 (1.1° away on the sky, at least 400,000 light-years from it), and 9 more.

By apparent size it is number 1 of the 12,657 galaxies on the Galaxy Origins register.