Hubble revisits a grand spiral

Today’s NASA/ESA Hubble Space Telescope Picture of the Week features the glorious spiral galaxy NGC 5643, which is located roughly 40 million light-years away in the constellation Lupus. NGC 5643 is what’s known as a grand design spiral, referring to how the galaxy’s two large, winding spiral arms are clear to see. The spiral arms are defined by bright blue stars, lacy reddish-brown dust clouds and pink star-forming regions.

As fascinating as the galaxy appears at visible wavelengths, some of NGC 5643’s most interesting features are invisible to the human eye. Ultraviolet and X-ray images and spectra of NGC 5643 show that the galaxy hosts an active galactic nucleus: an especially bright galactic core powered by a feasting supermassive black hole. When a supermassive black hole ensnares gas from its surroundings, the gas collects in a disc that heats up to hundreds of thousands of degrees. The superheated gas shines brightly across the electromagnetic spectrum, but especially at X-ray wavelengths.

NGC 5643’s active galactic nucleus isn’t the brightest source of X-rays in the galaxy, though. Researchers using ESA’s XMM-Newton discovered an even brighter X-ray-emitting object, called NGC 5643 X-1, on the galaxy’s outskirts. What could be a more powerful source of X-rays than a supermassive black hole? Surprisingly, the answer appears to be a much smaller black hole! While the exact identity of NGC 5643 X-1 is not yet known, evidence points to a black hole that is about 30 times more massive than the Sun. Locked in an orbital dance with a companion star, the black hole ensnares gas from its stellar companion, creating a superheated disc that outshines the galactic centre.

NGC 5643 was also the subject of a previous Picture of the Week. The new image incorporates additional wavelengths of light, including the red color that is characteristic of gas heated by massive young stars. 

[Image Description: A close-up of a spiral galaxy, seen face-on. Its center is a bright white point, surrounded by a large yellowish oval with thin lines of dust swirling in it. From the sides of the oval emerge two bright spiral arms which wind through the round disc of the galaxy, filled with shining pink spots where stars are forming and more dark reddish dust. Many stars can be seen in the foreground, over and around the galaxy.]