“The sign of our extinction would be nothing more than a game flying in the sky for a second,” said film director Stanley Kubrick, referring to an image of the destruction of our planet to an alien observer in the Andromeda Galaxy, a massive spiral system so close to our increasingly fragile earth that it appears as a cigar-shaped flicker of light high in the autumn night sky. The Hubble Space Telescope announced this week that it has captured our neighbor’s almost invisible halo, M31 – a diffuse plasma veil that extends 1.3 million light-years from the galaxy – about half our Milky Way – and up to 2 million light-years. in some directions.
At the landmark, scientists using NASA’s Hubble Space Telescope have mapped out the immense halo of gas, around the Andromeda Galaxy, our nearest large galactic neighbor discovered a complex and dynamic inner shell created by impact of supernova activity, which extends to about half a million light-years. “The outer shell,” says study leader Nicolas Lehner, an astrophysicist at the University of Notre Dame, “is smoother and hotter.”
Betrays a laugh structure
The Hubble team also found that the halo has a layered structure, with two main nests and distinct shells of gas. “Understanding the enormous halos of gas surrounding galaxies is very important,” said co-researcher Samantha Berek of Yale University in New Haven, Connecticut. “This reservoir of gas contains fuel for future star formation in the galaxy, as well as currents from events such as supernovae. It is full of clues as to the past and future evolution of the galaxy, and we are finally able to study it in detail in our nearest galactic neighbor.
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A signature of this activity is the team’s discovery of a large number of heavy elements in the gaseous halo of Andromeda. Heavier elements are sought out in the interior of stars and then thrown into space – sometimes violently when a star dies. The halo is then contaminated with this material from star explosions.
Ancient Light of 43 Quasars
Through a program called Project AMIGA (Andromeda Ionized Gas Absorption Map), the study examined the light of 43 quasars – the very distant, brilliant nuclei of active galaxies driven by black holes – that lie far beyond Andromeda. The quasars are scattered behind the halo, allowing scientists to study multiple regions. Looking through the halo to the light of the quasars, the team observed how this light is absorbed by the Andromeda halo and how that recording changes in different regions.
The incredible Andromeda halo is made of very rare and ionized gas that does not emit radiation that is easy to detect. Therefore, detecting the recording of light coming from a background source is a better way to examine this material.
The purple-tinted illustration of the halo of the Andromeda galaxy, with background quasars (shown in yellow dots) scattered throughout. This illustration shows the location of the 43 quasars that scientists used to study Andromeda’s gaseous halo. These quasars – the very distant, brilliant nuclei of active galaxies driven by black holes – are scattered far behind the halo, allowing scientists to study multiple regions. Looking through the incredible halo to the light of the quasars, the team observed how this light is absorbed by the halo and how that recording changes in different regions. By finding the recording of light coming from the background quasars, scientists can study the material of the halo. (NASA, ESA, and E. Wheatley, STScI)
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The researchers used the unique capability of Hubble’s Cosmic Origins Spectrograph (COS) to study the ultraviolet light of quasars. Ultraviolet light is absorbed by the Earth’s atmosphere, making it impossible to observe with telescopes on the ground. The team used COS to detect ionized gases of carbon, silicon and oxygen. An atom is ionized when radiation strikes one or more electrons.
The Probe of 2015
Andromeda’s halo has been previously investigated by Lehner’s team. In 2015, they discovered that the Andromeda halo is large and massive. But there was little hint of their complexity; now it has been mapped in more detail, leading to its size and mass being determined much more precisely.
“Previously, there was very little information – but six quasars – within 1 million light-years of the galaxy. This new program offers much more information about this inner region of the halo of Andromeda,” explained co-researcher J. Christopher Howk , also from Notre Dame. “Testing gas within this radius is important because it represents something of a gravitational force of influence for Andromeda.”
Similar to the Halo of Milky Way
Because we live in the Milky Way, scientists cannot easily interpret the signature of the glory of our own galaxy. However, they believe that the halos of Andromeda and the Milky Way should be very similar, because these two galaxies are quite similar. The two galaxies are on a collision course, and will merge to form a giant elliptical galaxy starting over 4 billion years from now.
Scientists have studied gaseous halos of distant galaxies, but those galaxies are much smaller in the sky, which means that the number of bright enough background quasars to study their halo is normally only one per galaxy. Spatial information is therefore essentially lost. With its proximity to Earth, Andromeda’s gaseous halo looms large in the sky, allowing for much more extensive sampling.
“This is truly a unique experiment, because we only have information with Andromeda about their halo along not just one or two lines of sight, but more than 40,” Lehner explained. “This is groundbreaking for capturing the complexity of a galaxy halo outside our own galaxy.”
In fact, Andromeda is the only galaxy in the universe for which this experiment can now be done, and only with Hubble. Only with an ultraviolet-sensitive future space telescope can scientists routinely conduct such experiments outside the approximately 30 galaxies of the Local Group. “So Project AMIGA has also given us a glimpse of the future,” Lehner said.
The Daily Galaxy, Sam Cabot, via NASA’s Goddard Space Flight Center
