The Whirlpool Galaxy is shaped by satellite galaxies passing through its disk. science news


An international team of researchers has demonstrated that the disk of the Whirlpool Galaxy (M51) is shaped by the repeated passage of the satellite galaxy NGC 5195 through its disk. The interaction defined the structure of the spiral arms and promoted star formation.

Whirlpool Galaxy with his partner. (Image credit: IAC).

New Delhi: The Whirlpool Galaxy is one of the most dramatic examples of a 'grand design' spiral galaxy, with a pair of well-defined spiral arms. The galaxy is 31 million light-years away, and is a face-to-face galaxy, meaning humans can see the entire galactic disk from their vantage point. The Whirlpool Galaxy has been continuously studied since its discovery in 1771, and is notable for having a companion galaxy, named NGC 5195, which is at the end of one of the spiral arms.

The spiral arms of the Whirlpool Galaxy contain stellar nurseries rich in star formation. As a result, energetic young stars occupy the spiral arms of the galaxy, caused by the compression of spiral density waves rotating in the galactic disk. These density waves are similar to the standing waves in musical instruments, but rotate around the axis of the rotating galaxy.

M51 infrared

Colored markers indicate density wave echoes. (Image credit: IAC).

New study confirms previous predictions

Previous theoretical studies had indicated the possibility that the Whirlpool Galaxy's well-defined shape was caused by its interaction with NGC 5195. In 2010, researchers published a paper suggesting that NGC 5195 had recently passed through M51's disk, and that the second encounter had caused twisting in each of the two spiral arms. Now, a team of international researchers has been able to confirm these predictions based on precise observations of the Whirlpool Galaxy using multiple ground- and space-based instruments.

A paper describing the findings has been published The Astrophysical Journal, Joan Font, first author of the paper, says, “Our work shows very clearly that the first passage of NGC 5195 created the two-armed structure of M51, which would have more strongly affected the interior of the disk and the southern arm. while the second path caused bending in the arms, which had a greater impact on the outer portion of the disc and the northern arm.


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