Adi Foord

We are pleased to welcome Adi Foord as a guest blogger. Adi is the first author of a pair of papers that are the subject of the latest Chandra press release. She is a Post postdoctoral fellow at the Kavli Institute of Particle Astrophysics and Cosmology at Stanford University. She received her bachelor's degree in Physics & Astronomy from Boston University in 2014, and recently received her Ph.D. in Astronomy & Astrophysics from the University of Michigan (Summer 2020). Adi is a high-energy astrophysicist who is interested in how and which environmental properties impact supermassive black hole accretion and evolution. Most of her work uses X-ray observations of supermassive black holes, and she is currently focusing on systems where two supermassive black holes are in the process of merging.

With the advancement of gravitational wave detectors such as LIGO, we are starting to get real proof that black holes exist, and that some evolve over time via mergers with other black holes. The black holes that gravitational wave detectors like LIGO study are solar mass black holes. As the name and unit imply, these black holes have masses between about five and 100 times that of the sun, and are believed to be formed after the death of a massive star. But what about supermassive black holes, the massive counterparts to solar mass black holes that lie at the center of most massive galaxies? With the groundbreaking image supplied by the Event Horizon Telescope (EHT) in April 2019, we were given proof that supermassive black holes exist as well. But in order to have proof that they merge, and emit gravitational waves, we will have to wait for results from pulsar timing arrays (PTAs) and space-based interferometry (such as LISA). This is because the expected gravitational wave frequencies the supermassive black hole mergers are theorized to emit are outside the range of LIGO.

Magnetar J1818.0-1607
Credit: X-ray: NASA/CXC/Univ. of West Virginia/H. Blumer;
Infrared (Spitzer and Wise): NASA/JPL-CalTech/Spitzer

In 2020, astronomers added a new member to an exclusive family of exotic objects with the discovery of a magnetar. New observations from NASA's Chandra X-ray Observatory help support the idea that it is also a pulsar, meaning it emits regular pulses of light.

Magnetars are a type of neutron star, an incredibly dense object mainly made up of tightly packed neutrons, which forms from the collapsed core of a massive star during a supernova.

What sets magnetars apart from other neutron stars is that they also have the most powerful known magnetic fields in the Universe. For context, the strength of our planet's magnetic field has a value of about one Gauss, while a refrigerator magnet measures about 100 Gauss. Magnetars, on the other hand, have magnetic fields of about a million billion Gauss. If a magnetar was located a sixth of the way to the Moon (about 40,000 miles), it would wipe the data from all of the credit cards on Earth.

Abell 2261
Credit: X-ray: NASA/CXC/Univ of Michigan/K. Gültekin;
Optical: NASA/STScI and NAOJ/Subaru; Infrared: NSF/NOAO/KPNO

The mystery surrounding the whereabouts of a supermassive black hole has deepened.

Despite searching with NASA's Chandra X-ray Observatory and Hubble Space Telescope, astronomers have no evidence that a distant black hole estimated to weigh between 3 billion and 100 billion times the mass of the Sun is anywhere to be found.

This missing black hole should be in the enormous galaxy in the center of the galaxy cluster Abell 2261, which is located about 2.7 billion light years from Earth. This composite image of Abell 2261 contains optical data from Hubble and the Subaru Telescope showing galaxies in the cluster and in the background, and Chandra X-ray data showing hot gas (colored pink) pervading the cluster. The middle of the image shows the large elliptical galaxy in the center of the cluster.

View Wavelengths
Sonification Credit: NASA/CXC/SAO/K. Arcand, SYSTEM Sounds (M. Russo, A. Santaguida)

A new trio of examples of 'data sonification' from NASA missions provides a new method to enjoy an arrangement of cosmic objects. Data sonification translates information collected by various NASA missions — such as the Chandra X-ray Observatory, Hubble Space Telescope, and Spitzer Space Telescope — into sounds.

This image of the Bullet Cluster (officially known as 1E 0657-56) provided the first direct proof of dark matter, the mysterious unseen substance that makes up the vast majority of matter in the Universe. X-rays from Chandra (pink) show where the hot gas in two merging galaxy clusters has been wrenched away from dark matter, seen through a process known as "gravitational lensing" in data from Hubble (blue) and ground-based telescopes. In converting this into sound, the data pan left to right, and each layer of data was limited to a specific frequency range. Data showing dark matter are represented by the lowest frequencies, while X-rays are assigned to the highest frequencies. The galaxies in the image revealed by Hubble data, many of which are in the cluster, are in mid-range frequencies. Then, within each layer, the pitch is set to increase from the bottom of the image to the top so that objects towards the top produce higher tones.

IC 4593
Credit: X-ray: NASA/CXC/Columbia Univ./A. Johnson et al.; Optical: NASA/STScI

On Earth, amethysts can form when gas bubbles in lava cool under the right conditions. In space, a dying star with a mass similar to the Sun is capable of producing a structure on par with the appeal of these beautiful gems.

As stars like the Sun run through their fuel, they cast off their outer layers and the core of the star shrinks. Using NASA's Chandra X-ray Observatory, astronomers have found a bubble of ultra-hot gas at the center of one of these expiring stars, a planetary nebula in our galaxy called IC 4593. At a distance of about 7,800 light years from Earth, IC 4593 is the most distant planetary nebula yet detected with Chandra.

This new image of IC 4593 has X-rays from Chandra in purple, invoking similarities to amethysts found in geodes around the globe. The bubble detected by Chandra is from gas that has been heated to over a million degrees. These high temperatures were likely generated by material that blew away from the shrunken core of the star and crashed into gas that had previously been ejected by the star.

Barnard's Star (GJ 699)
Credit: X-ray light curve: NASA/CXC/University of Colorado/K. France et al.;
Illustration: NASA/CXC/M. Weiss

A new study using data from NASA's Chandra X-ray Observatory and Hubble Space Telescope gives new insight into an important question: how habitable are planets that orbit the most common type of stars in the Galaxy? The target of the new study, as reported in our press release, is Barnard's Star, which is one of the closest stars to Earth at a distance of just 6 light years. Barnard's Star is a red dwarf, a small star that slowly burns through its fuel supply and can last much longer than medium-sized stars like our Sun. It is about 10 billion years old, making it twice the age of the Sun.

The authors used Barnard's Star as a case study to learn how flares from an old red dwarf might affect any planets orbiting it. This artist's illustration depicts an old red dwarf like Barnard's Star (right) and an orbiting, rocky planet (left).

4U 1916-053, spectrum & illustration
Credit: Spectrum: NASA/CXC/University of Michigan/N. Trueba et al.; Illustration: NASA/CXC/M. Weiss

What do Albert Einstein, the Global Positioning System (GPS), and a pair of stars 200,000 trillion miles from Earth have in common?

The answer is an effect from Einstein's General Theory of Relativity called the "gravitational redshift," where light is shifted to redder colors because of gravity. Using NASA's Chandra X-ray Observatory, astronomers have discovered the phenomenon in two stars orbiting each other in our galaxy about 29,000 light years (200,000 trillion miles) away from Earth. While these stars are very distant, gravitational redshifts have tangible impacts on modern life, as scientists and engineers must take them into account to enable accurate positions for GPS.

While scientists have found incontrovertible evidence of gravitational redshifts in our solar system, it has been challenging to observe them in more distant objects across space. The new Chandra results provide convincing evidence for gravitational redshift effects at play in a new cosmic setting.

Shifu Zhu

Shifu Zhu, a 5th-year graduate student of Astronomy & Astrophysics at Pennsylvania State University, is our guest blogger for this post. He received his B.S. in Astronomy from the University of Science and Technology of China (USTC) in 2013. He received his M.S. in Astrophysics from USTC in 2016.

“So, the answer to the nature of the X-ray emission from radio-loud quasars is simpler than we previously had thought,” I said to myself after staring for a while at our new correlations between how bright radio-loud quasars are in X-ray and ultraviolet light.

The term “quasar” was originally coined for bright radio sources that look like stars in visible-light images, i.e., quasi-stellar radio sources. Shortly after their discovery, researchers realized that quasars are supermassive black holes (with masses of millions to billions of times that of the Sun) feeding on material that is gravitationally attracted to them. Notably, despite this strong gravitational attraction, some material can also be ejected in powerful jets, narrow streams of material shooting away from the supermassive black hole in opposite directions. These jets are fueled by material in an “accretion disk” falling towards the black hole.

Sagittarius A*
Credit: NASA/CXC

The winners of the 2020 Nobel Prize in Physics were announced this week: a trio of astrophysicists won for their work — both theoretical and observational — of black holes. Two of the three, Dr. Andrea Ghez of the University of California at Los Angeles and Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics in Germany — were cited “for the discovery of a supermassive compact object at the center of our galaxy”.

There are black holes throughout our Galaxy and across the Universe, but the one at the Milky Way's center, known as Sagittarius A* (Sgr A*), is particularly fascinating. At a distance of about 26,000 light years from Earth, Sgr A* is the closest supermassive black hole to us. Both Ghez and Genzel have spent decades tracking stars and clouds of dust near Sgr A* to learn more about the black hole and its environment.

Explore Solos
Sonification Credit: NASA/CXC/SAO/K. Arcand, SYSTEM Sounds (M. Russo, A. Santaguida)

The center of our Milky Way galaxy is too distant for us to visit in person, but we can still explore it. Telescopes give us a chance to see what the Galactic Center looks like in different types of light. By translating the inherently digital data (in the form of ones and zeroes) captured by telescopes in space into images, astronomers create visual representations that would otherwise be invisible to us.

But what about experiencing these data with other senses like hearing? Sonification is the process that translates data into sound, and a new project brings the center of the Milky Way to listeners for the first time. The translation begins on the left side of the image and moves to the right, with the sounds representing the position and brightness of the sources. The light of objects located towards the top of the image are heard as higher pitches while the intensity of the light controls the volume. Stars and compact sources are converted to individual notes while extended clouds of gas and dust produce an evolving drone. The crescendo happens when we reach the bright region to the lower right of the image. This is where the 4-million-solar-mass supermassive black hole at the center of the Galaxy, known as Sagittarius A* (A-star), resides, and where the clouds of gas and dust are the brightest.

Users can listen to data from this region, roughly 400 light years across, either as "solos" from NASA's Chandra X-ray Observatory, Hubble Space Telescope, and Spitzer Space Telescope, or together as an ensemble in which each telescope plays a different instrument. Each image reveals different phenomena happening in this region about 26,000 light years from Earth. The Hubble image outlines energetic regions where stars are being born, while Spitzer's infrared image shows glowing clouds of dust containing complex structures. X-rays from Chandra reveal gas heated to millions of degrees from stellar explosions and outflows from Sagittarius A*.

In addition to the Galactic Center, this project has also produced sonified versions of the remains of a supernova called Cassiopeia A, or Cas A, and the "Pillars of Creation" located in Messier 16.