N44C, an emission nebula in the LMC

 
N44C, an emission nebula in the LMC

Image Credit: Donald Garnett (University of Arizona) et al., Hubble Heritage Team (STScI/AURA) and NASA

N44C is an emission nebula of about 125 light-years across in the Large Magellanic Cloud, a small companion galaxy to our own Milky Way which lies about 157,000 light-years away in the southern constellation of Dorado, while it is receding from us at approximately 278 kilometers per second. The nebula is surrounding an association of young stars.

N44C is part of the larger N44 (LHA 120-N 44) complex, which includes young, hot, massive stars, nebulae, and a “superbubble” blown out by multiple supernova explosions. Part of the superbubble is seen in red at the very bottom left of this image.

Nebulae are huge clouds of gas and dust, the cosmic material from which stars and planets form. Many of them (including planetary nebulae and supernova remnants) emit the light of the star(s) within them, and are then called emission nebulae. For comparison, reflection nebulae reflect the light of a nearby star or stars. The energy from the nearby star(s) is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust visible.

In N44C, softly glowing filaments of ionized hydrogen gas are streaming from the complex of young stars. But there are two theories about the star that is mainly responsible for illuminating the nebula:

1) The star is unusually hot. While the most massive stars, ranging from 10-50 times more massive than the Sun, have maximum temperatures of 54,000 to 90,000 degrees Fahrenheit (30,000 to 50,000 degrees Kelvin), the star illuminating N44C appears to be significantly hotter, with a temperature of about 135,000 degrees Fahrenheit (75,000 degrees Kelvin)!

Ideas proposed to explain this unusually high temperature include the possibility of a neutron star or black hole that intermittently produces X-rays but is now “switched off.”

2) The star, although young and bright, does not seem hot enough to create some of the colors observed. (A search for a hidden hotter star in X-rays has come up empty.)

In this case it might be that the known central star has a neutron star companion in a very wide orbit. Hot X-rays might only then be emitted during brief periods when the neutron star nears the known star and crashes through a disk of surrounding gas. Future observations might tell.

The data for this image were taken in November 1996 with Hubble’s Wide Field Planetary Camera 2 by Donald Garnett (University of Arizona) and collaborators and stored in the Hubble archive. The image was composed by the Hubble Heritage Team (STScI/AURA).

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