What does a dead galaxy look like? The NASA Hubble Space Telescope's latest discovery revealed six galaxies that ran out of cold hydrogen gas and are unable to make new stars. The celestial phenomenon left researchers shocked and a lot of space fans are fascinated. Arguably, these six dead galaxies look incredibly amazing.

A healthy galaxy is a dust-and-gas-rich galaxy. Frontiers explained that galaxies create sun-like stars using gas and dust. Together, gas and dust generate gas clouds that collapse and reform due to gravity. The cycle repeats for a million years until the gas cloud begins to shine like the Sun. Leftover materials from the star's birth are used to create planets and other space objects that orbit around the star.

With that in mind, researchers found something odd in space. NASA's Hubble Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA) captured six young, massive, "dead" galaxies that ran out of cold hydrogen gas. The cosmic phenomenon was immediately published in the Nature journal.

NASA Hubble Images: 6 Massive 'Dead' Galaxies Found!

Hubble tweeted its amazing discovery early on Tuesday. The post said, "Astronomers discovered six massive, "dead" galaxies that had run out of the cold hydrogen gas needed to make stars." The tweet also contained four images, with the left images at "regular" size and the right images as "zoomed in" sections of space.

NASA explained that yellow traces on the image show the glow of starlight. The artificial purple color represents traces of cold dust found in ALMA's observation. The cold dust is also a proxy for the cold hydrogen gas needed for star formation.

On image MRG-M1341, the purple blob to the left of the galaxy is a dust-and-gas-rich image. In comparison, image MRG-M1341 only has very little gas and dust at its center. Researchers suggest that the star formation sequence for this galaxy already shut down.

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All six dead galaxies found don't appear to rejuvenate, even through minor mergers and accretions from nearby galaxies and gas.

Researchers are confused with this development. They do not know how this celestial phenomenon happened. According to NASA, assistant professor of astronomy at the University of Massachusetts, Kate Whitaker, proposed several theories. "Did a supermassive black hole in the galaxy's center turn on and heat up all the gas? If so, the gas could still be there, but now it's hot. Or it could have been expelled and now it's being prevented from accreting back onto the galaxy. Or did the galaxy just use it all up, and the supply is cut off? These are some of the open questions that we'll continue to explore with new observations down the road."

NASA Hubble Space Telescope and REQUIEM Program

Hubble and ALMA's latest discovery was part of the ongoing REQUIEM program, which stands for Resolving QUIEscent Magnified Galaxies At High Redshift.

Combining technologies between Hubble and ALMA, the REQUIEM team plans to study more about the formation of these six galaxies and other galaxy clusters in the distant space.

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