A whole galaxy acting as a megamaser

IRAS 16399-0937 (Image ESA/Hubble & NASA. Acknowledgement: Judy Schmidt (geckzilla))
IRAS 16399-0937 (Image ESA/Hubble & NASA. Acknowledgement: Judy Schmidt (geckzilla))

An image obtained thanks to observations made by the Hubble Space Telescope shows a very peculiar galaxy. Called IRAS 16399-0937, it’s a megamaser, which is an astronomical maser that emits microwaves with an intensity about a hundred million times greater than that of astronomical masers found in galaxies like the Milky Way. That’s because virtually all the galaxy is a maser.

A maser is similar to a laser but instead of visible light it emits microwaves. We got used to thinking of masers and lasers as artificial devices, however, maser emission sources that are natural can exist. There are different types of them with a wide range of intensity. That’s why very intense maser sources are called a megamaser or even a gigamaser.

IRAS 16399-0937, also known as LEDA 58817 or 2MASX J16424018-0943192, is a galaxy about 370 million light years away from Earth that turned out to be really interesting for its various features. The Hubble Space Telescope observed this galaxy at different wavelengths using two instruments: the Advanced Camera for Surveys (ACS) and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

Thanks to the NICMOS instrument’s high sensitivity, resolution and field of view, the astronomers were able to observe the structure’s details of the galaxy IRAS 16399-0937 finding that has a double nucleus. The most plausible explanation is that the structure is the result of an ongoing merger between two different galaxies. The astronomers caught that process while is under way and actually it seems to be in its first phase because you can still see the differences between the two galaxies that are merging.

Since the two original galaxies are still mostly separated, they were called IRAS 16399N the northern one and IRAS 16399S the southern one. They’re buried in the same swirl of gast and dust and are interacting with stars and interstellar clouds that attract each other with their gravity force. At the same time, the exam of the two nuclei allowed to note that they’re very different.

IRAS 16399N is of the type called a starburst galaxy, that is, the type in which a very intense star formation process is taking place. Peaks of star formation can also take place due to galactic collisions so this might be one of these cases. This galactic nucleus is home to a supermassive black hole with a mass estimated at one hundred million solar masses.

IRAS 16399S is instead classified as a LINER (Low Ionization Nuclear Emission Region), a type of galactic nucleus which has an emission generated mainly from neutral or weakly ionized atoms. It’s a common occurrence among elliptical or lenticular galaxies but the sources of energy and the ionization mechanism are reasons of discussion among scientists.

IRAS 16399-0937 is therefore a very interesting object of study for astronomers because we have two galaxies that are currently merging and each of them contains objects that are worth studying, a supermassive black hole about 25 times more massive than the Milky Way’s one and the new galaxy that is forming is a megamaser.

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