Trying into the dusty core of a galaxy to review an lively supermassive black gap – what’s mistaken with it?
From NASA
March 17, 2021
Researchers using NASA’s upcoming James Webb Space Telescope will map and model the core of the nearby Centaurus A galaxy.
Centaurus A is a giant of a galaxy, but its telescopic appearance can be deceiving. Dark trails of dust and young blue star clusters running through the central area can be seen in the ultraviolet, visible, and near infrared light, and paint a fairly subdued landscape. With the switch to X-ray and radio light views, however, a much rougher scene is beginning to unfold: From the core of the misshapen elliptical galaxy, spectacular rays of material have broken out of its active supermassive black hole – known as the active galactic core. Send material far beyond the boundaries of the galaxy into space.
Centaurus A has a warped central disk of gas and dust, evidence of a past collision and merger with another galaxy. It also has an active galactic core that regularly emits jets. It is the fifth brightest galaxy in the sky and only about 13 million light years from Earth. This makes it an ideal target to study an active galactic core – a supermassive black hole that emits jets and winds – with NASA’s upcoming James Webb Space Telescope. Credits: X-ray: NASA / CXC / SAO; visual: Rolf Olsen; Infrared: NASA / JPL-Caltech; Radio: NRAO / AUI / NSF / Univ.Hertfordshire / M.Hardcastle
What exactly is happening at the core to bring about all of these activities? The upcoming observations by Nora Lützgendorf and Macarena García Marín of the European Space Agency with NASA’s James Webb Space Telescope will allow researchers to look through their dusty core for the first time in high resolution to answer these questions.
“There’s so much going on in Centaurus A,” explains Lützgendorf. “The galaxy’s gas, disk and stars all move under the influence of its central supermassive black hole. With the galaxy so close to us, we can use Webb to create two-dimensional maps to see how the gas and stars move in their central region, how they are affected by the jets of their active galactic core, and ultimately, better mass characterize its black hole. “
Centaurus A’s dusty core is visible in visible light, but its rays are best seen in X-ray and radio light. With the upcoming infrared observations from NASA’s James Webb Space Telescope, the researchers hope to better determine the mass of the galaxy’s central supermassive black hole and gain clues as to where the jets were ejected. Credits: X-ray: NASA / CXC / SAO ;; visual: Rolf Olsen; Infrared: NASA / JPL-Caltech; Radio: NRAO / AUI / NSF / Univ.Hertfordshire / M.Hardcastle
A quick look back
Let’s click “Rewind” to see a little bit of what is already known about Centaurus A. It’s well studied because it’s relatively close – roughly 13 million light years away – which means we can clearly resolve the entire galaxy. The first record was recorded in the mid-19th century, but astronomers lost interest until the 1950s because the galaxy appeared to be a calm, albeit misshapen, elliptical galaxy. When researchers could begin observing with radio telescopes in the 1940s and 1950s, Centaurus A became radically more interesting – and its jets came into view. In 1954, researchers found that Centaurus A was the result of two galaxies joining together, which was later estimated 100 million years ago.
With more observations in the early 2000s, the researchers estimated that its active galactic core launched twin jets in opposite directions about 10 million years ago. When examining the entire electromagnetic spectrum, from X-ray to radio light, it is clear that this story has much more to learn.
“Multi-wavelength studies of any galaxy are like the layers of an onion. Each wavelength shows you something different, ”said Marín. “With Webb’s instruments in the near and mid-infrared, we see much colder gas and dust than in previous observations and learn a lot more about the environment at the center of the galaxy.”
Supermassive black holes, which lie in the center of galaxies, are insatiable. They regularly “slurp” or “swallow” from the swirling discs of gas and dust that orbit them, which can lead to massive runoffs that affect star formation locally and further away. When NASA’s James Webb Space Telescope begins observing the cores of galaxies, its infrared instruments penetrate the dust and provide images and incredibly high-resolution data that researchers can use to learn exactly how one process triggers another and how they create a huge feedback loop .Credits: NASA, ESA and L. Hustak (STScI)
Visualization of the Webb data
The team, led by Lützgendorf and Marín, will not only observe Centaurus A by taking pictures with Webb, but also collect data known as spectra that propagate the light into its wavelength components like a rainbow. Webb’s spectra will provide high resolution information about the temperatures, velocities and compositions of the material in the center of the galaxy.
In particular, Webb’s near-infrared spectrograph (NIRSpec and Mid-Infrared Instrument (MIRI)) offers the research team a combination of data: an image plus a spectrum from each pixel of that image. In this way, the researchers can create complicated 2D images from the spectra, which they can use to see what is going on behind the dust veil in the middle – and analyze them from many angles.
Compare this modeling style to analyzing a garden. In the same way that botanists classify plants based on certain characteristics, these researchers will classify spectra from Webb’s MIRI to construct “gardens” or models. “If you take a snapshot of a garden from a great distance,” Marín explained, “you will see something green, but with Webb we can see individual leaves and flowers, their stems and possibly the soil below. ”
While studying the spectra, the research team creates maps of parts of the garden and compares one spectrum with another nearby spectrum. This is analogous to determining which parts contain which plant species, based on comparisons of “stems”, “leaves” and “flowers”.
“We do a lot of comparisons in spectral analysis,” continued Marín. “If I compare two spectra in this region, I may find that what I observed contains a prominent population of young stars. Or confirm which areas are both dusty and heated. Or maybe we are identifying the emission coming from the active galactic core. “
In other words, the “ecosystem” of spectra has many layers that allow the team to better define exactly what is there and where it is – which is made possible by Webb’s specialized infrared instruments. And since these studies will build on many previous studies, researchers can confirm new features, refine them, or break new ground.
Watch how the jets and winds of a supermassive black hole affect its host galaxy – and space hundreds of thousands of light years away over millions of years. Credits: NASA, ESA and L. Hustak (STScI)
Weighing the black hole in Centaurus A.
The combination of images and spectra from NIRSpec and MIRI enables the team to create very high resolution maps of the gas and star velocities in the center of Centaurus A. “We plan to use these maps to model the entire hard drive in the center of the galaxy is moving in order to determine the mass of the black hole more precisely,” explains Lützgendorf.
Since the researchers understand how a black hole’s gravity determines the rotation of nearby gas, they can use the Webb data to weigh the black hole in Centaurus A. With a more complete set of infrared data, they also determine whether different parts of the gas are all behaving as expected. “I’m looking forward to filling out our details in full,” said Lützgendorf. “I hope to see how the ionized gas acts and swirls and where we see the jets.”
The researchers also hope to break new ground. “It is possible that we will find things that we have not yet thought about,” explains Lützgendorf. “In some respects, we will open up completely new areas with Webb.” Marín fully agrees, adding that building on a wealth of existing data is invaluable. “The most exciting aspect of these observations is the potential for new discoveries,” she said. “I think we could find something that would make us look back at other data and reinterpret what was seen earlier.”
These Centaurus A studies are being conducted by Gillian Wright and Pierre Ferruit as part of the joint MIRI and NIRSpec Guaranteed Time Observations programs. All of Webb’s data is ultimately stored in the publicly accessible Barbara A. Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute in Baltimore.
The James Webb Space Telescope will be the world’s premier space science observatory when it launches in 2021. Webb will solve puzzles in our solar system, look beyond distant worlds around other stars and investigate the mysterious structures and origins of our universe and our location in there. Webb is an international program led by NASA with its partners ESA (European Space Agency) and Canadian Space Agency.
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