A team of scientists recently made a $150,000 gamble by pointing the Keck telescope at Mauna Kea Observatory in Hawai’i towards what appeared to be empty space. Their hope was to uncover the hidden gas that surrounds galaxies in the universe. To their delight, their gamble paid off, and they were able to capture the first detailed image of the gas shroud around a galaxy. This discovery has significant implications for understanding the composition and interactions of galaxies.
Contrary to popular belief, the majority of matter in the universe is not found in the bright stars that we typically associate with galaxies. Dark matter, an exotic invisible particle, surrounds galaxies and accounts for a significant portion of the universe’s matter. Additionally, large clouds of gas, known as halos, envelop galaxies and contain around 70-90% of the universe’s normal matter, consisting of hydrogen, helium, carbon, nitrogen, and oxygen gas.
These gas halos play a crucial role in the formation of stars and planets. However, they are extremely faint, about 10,000 to 100,000 times dimmer than the brighter parts of galaxies. Astronomers have known about these halos since the 1950s when they discovered that they absorb certain frequencies of light. However, until now, they had limited knowledge about the size, shape, and flow of gas within these halos.
The breakthrough came with the development of a new spectrograph called an “image slicer.” This device allowed scientists to capture spectroscopic images of the night sky at much fainter levels than previous instruments. The Keck Cosmic Web Imager, an ultra-faint spectrograph, was installed on the Keck telescope, one of the world’s largest optical telescopes located in Hawai’i. With this new technology, the team was able to observe and analyze the data from the seemingly empty space around a galaxy.
The team’s findings confirmed that the majority of the universe’s ordinary matter resides in these diffuse halos of gas. They also discovered that the transition from the galaxy to the halo is abrupt, rather than a smooth fade. This observation resolves previous debates about the nature of this transition.
However, the researchers are still puzzled as to why the gas halo emits a glow. Inside a galaxy, the glow of hydrogen gas is attributed to the heating from nearby stars. But outside a galaxy, there are not enough nearby stars to explain the observed glow. One possibility is that the halo is composed of streams of gas moving in different directions, and when they collide at high speeds, they emit light. Another theory suggests that the presence of very heavy stars and certain black holes within galaxies produce significant amounts of ultraviolet light, which could escape and contribute to the ambient background UV lighting of the cosmos.
Further observations and research are needed to fully understand the mechanisms behind the glow of the gas halo. Nonetheless, this groundbreaking study provides valuable insights into the composition and dynamics of galaxies, shedding light on our own cosmic story.
