After some time I am continuing my series of short posts about random Messier's objects. For this post random generator was @escapist and she chose very a special number - 99.
Messier 99 (M99), also known as the Coma Pinwheel is an unbarred spiral galaxy in constellation Coma Berenices inside the Virgo Cluster and it is approximately 15 MPc (15 mega parsecs or 56 million light-years) away from Milky Way. It has apparent magnitude 10.4 and lies at about 56 million light years away from Earth.
M99 rotates clockwise and is classified as an Sc type spiral galaxy (Hubble tuning fork). It has a diameter of about 85,000 light years and recedes from us at an unusually high velocity of 2,407 km/s. This is the highest redshift recorded for any Messier object.
It is one of the brighter spiral galaxies in the Virgo Cluster and appears almost face-on. It is very popular amongst astronomers, both professional and amateur, and best conditions to observe it are during the spring.
It has completely unbarred core and two giant spiral arms. One of the spiral arms is normal while the other one appears slightly distorted. Pinwheel is also asymmetric in shape, with the nucleus shifted from the galaxy’s centre. This asymmetry is most likely to be a result of gravitational interactions with other galaxies inside the Virgo Cluster.
Even though the Virgo Cluster Pinwheel has a diameter almost the same size as the Milky Way – with an estimated mass of 50 billion solar masses, it has only 5 percent of our galaxy’s mass.
This phenomenon is still a mystery for astrophysicists, but it could be the consequence of a close encounter with VIRGO HI21, which is an extended region of neutral hydrogen (HI) and a dark galaxy. Since we have no evidence of dark galaxy existence there is a possibility that M99 interacted with lenticular galaxy NGC 4262 back in the past, about 280 million years ago. Another significant result of the encounter is the star formation rate(SFR) which is about three times greater than SFR in other Sc galaxies.