The Hubble Space Telescope has captured, for the first time, blue gas being pushed out as if fleeing from a galaxy's center. The National Aeronautics and Space Administration (NASA) released on Jan. 2 (local time) a photo taken by Hubble of the galaxy NGC 4388, located about 60 million light-years (one light-year is the distance light travels in one year, about 9.46 trillion kilometers) from Earth. In the image, a blue-tinged column of gas extends from the core toward the lower right corner.
The Hubble Space Telescope is the first space telescope jointly developed and operated by NASA and the European Space Agency (ESA). Launched aboard the space shuttle Discovery in 1990, it orbits about 600 kilometers above Earth, observing the universe without atmospheric interference. Although its original design life was 15 years, ongoing maintenance has kept it active alongside the James Webb Space Telescope (JWT), launched in 2021.
◇ Capturing high-energy gas pushed out by a galaxy
The Hubble image shows NGC 4388, a member of the Virgo Cluster. The Virgo Cluster contains more than 1,000 galaxies and is the nearest large cluster to the Milky Way. NGC 4388 is a spiral galaxy, but because this image is taken from nearly edge-on, it appears as a long bar.
The galaxy's disk contains pink light from star-forming nebulae and blue light from clusters of hot stars. Thick dust clouds block the galaxy's intense white light at its center. The blue gas column at the lower right captured by Hubble this time was not visible in Hubble's 2016 image. NASA scientists suggested that the blue gas column outflowing from the galaxy originated in high-energy material permeating the space between galaxies.
The vast universe may appear empty aside from galaxies where stars are born and gather, but in reality this space is filled with hot gas known as the "intracluster medium." As NGC 4388 moves within the Virgo Cluster, it plows through this intracluster medium. The pressure from this medium then causes gas to stream out behind it. It is like pressing a PET bottle filled with carbonated gas and having cola spurt out.
The intracluster medium is high-energy plasma. Plasma refers to a state in which atomic nuclei and electrons are separated at extremely high temperatures. The intracluster medium consists of hydrogen and helium in a plasma state. Where, then, did the energy that makes this gas cloud glow as plasma come from? Scientists suspect it came from the supermassive black hole at the galaxy's center.
◇ The Virgo Cluster first showed the appearance of a black hole
A black hole is a celestial object whose gravitational pull is so strong that it draws in all matter. Such black holes reside at the centers of galaxies. Matter drawn into a black hole is compressed by gravity into a disk and rotates at near the speed of light. The radiation released at this time can ionize the nearest gas in the galaxy into a charged plasma state.
Coincidentally, the Virgo Cluster is also where humanity first saw the reality of a black hole. The international Event Horizon Telescope (EHT) collaboration in 2019 released an image of the M87 black hole at the center of the galaxy NGC 4486. By contrast, the black hole depicted in the film "Interstellar" was a computer-generated visualization based on physics theory, not an actual image.
In April 2017, the EHT team simultaneously observed the M87 black hole at the heart of the Virgo Cluster using radio telescopes at eight sites around the globe, including the South Pole and the Andes. The M87 black hole has a mass 6.5 billion times that of the sun. Such an enormous mass concentrated in one place produces gravity of unimaginable strength.
A black hole absorbs even light, so it cannot be photographed directly. Scientists instead photographed its shadow. The bright light seen in the image comes from matter rotating as it is pulled into the black hole, and the dark region within is the shadow left by the black hole. The black hole image released at the time matched perfectly with what Einstein predicted with the theory of relativity 100 years earlier.
Curiously, the lower part appears brighter in the black hole image. Matter close to the black hole rotates at near light speed before being drawn in. According to Einstein's theory of relativity released in 1915, the portion of the rotating disk moving toward Earth appears brighter than the portion moving away. It is the same principle as a siren sounding louder as an ambulance approaches and quieter as it passes.
References
NASA (2026), https://www.nasa.gov/image-article/hubble-glimpses-galactic-gas-making-a-getaway/
NASA (2016), https://science.nasa.gov/missions/hubble/hubble-catches-a-transformation-in-the-virgo-constellation/
The Astrophysical Journal Letters (2019), DOI: https://doi.org/10.3847/2041-8213/ab0ec7