Dwarf galaxy caught plunging into spiral

The mystery of a 'distubred' spiral galaxy may have been solved, following the discovery of an elongated dwarf nearby.

Published: February 29, 2016 at 12:00 pm

Spiral galaxy NGC 253 is seen here with the newly-discovered dwarf galaxy NGC 253-dw2 in the top left. The elongated shape of the dwarf implies it is being pulled apart by the spiral galaxy, which itself shows disturbances about its edge that could be caused by the interaction. Credit: Copyright © 2015 R. Jay GaBany (Cosmotography.com) & Michael Sidonio. Insert image: R. Jay GaBany & Johannes Schedler 2019


Astronomers may have caught a dwarf galaxy in the act of plunging into a spiral galaxy and disrupting its structure.

NGC 253 is located in the southern constellation of Sculptor about 11 million lightyears from Earth.

The spiral galaxy already appeared to show signs of having been disturbed by a dwarf galaxy, but no such culprit was ever discovered.

The new discovery of dwarf galaxy NGC 253-dw2, however, may have solved the problem.

The two objects are separated from each other by a distance of about 160,000 lightyears, yet are still close enough that the dwarf has an elongated appearance, probably caused by the gravitational pull of the larger spiral.

"The outer regions of giant galaxies like our own Milky Way appear to be a jumble of debris from hundreds of smaller galaxies that fell in over time and splashed into smithereens," says Aaron Romanowsky of San José State University, who led the study.

"These dwarfs are considered building blocks of the giants, but the evidence for giants absorbing dwarfs has been largely circumstantial.

Now we have caught a pair of galaxies in the act of a deadly embrace."

"The dwarf has been trapped by its giant host and will not survive intact for much longer," says team member Nicolas Martin, of the Strasbourg Observatory.

"The next time it plunges closer to its host, it could be shredded into oblivion.

However, the host may suffer some damage too, if the dwarf is heavy enough."

The discovery began using a digital image of the spiral galaxy taken by astrophotographer Michael Sidonio and followed up with further observations.

Eventually, the Subaru telescope in Hawaii was used to identify the galaxy.

"In the first image, we weren't sure if there was really a faint galaxy or if it was some kind of stray reflection," says David Martínez-Delgado from Heidelberg University.

"With the high-quality imaging of the Suprime-Cam instrument on the Subaru Telescope, we can now see that the smudge is composed of individual stars and is a bona fide dwarf galaxy.


This discovery is a wonderful example of fruitful collaboration between amateur and professional astronomers."

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