Space News & Blog Articles

A Chandra X-ray Observatory view of the supermassive black hole at the heart of quasar H1821+643. Courtesy NASA/CXC/Univ. of Cambridge/J. Sisk-Reynés et al.

Black holes. They used to be theoretical, up until the first one was found and confirmed back in the late 20th Century. Now, astronomers find them all over the place. We even have direct radio images of two black holes: one in M87 and Sagittarius A* in the center of our galaxy. So, what do we know about them? A lot. But, there’s more to find out. A team of astronomers using Chandra X-ray Observatory data has made a startling discovery about a central supermassive black hole in a quasar embedded in a distant galaxy cluster. What they found provides clues to the origin and evolution of supermassive black holes.

Two-factor Identification of Black Holes

If you’re going to study a black hole, particularly a supermassive one, there are a lot of challenges. It turns out every large galaxy has a central monster black hole. So, it’s important to know as much as we can about them. These cosmic behemoths contain millions or even billions of solar masses. They have strong gravitational pulls—and nothing, not even light, can escape their clutches. That affects our ability to look at them and their nearby regions.

One thing that isn’t quite clear yet: how do these monsters form and evolve? The answer lies partially in two of their characteristics. “Every black hole can be defined by just two numbers: its spin and its mass,” said Julia Sisk-Reynes {Institute of Astronomy (IoA), the University of Cambridge in the U.K), who led a new study of a supermassive black hole some 3.6 billion years away from us. “While that sounds fairly simple, figuring those values out for most black holes has proved to be incredibly difficult.”

X-raying a Black Hole

Measuring the masses is difficult, although there are ways to do it. Measuring spin is a real challenge. To learn more about monster black holes, Sisk-Reynes and collaborators used Chandra X-ray Observatory data. They studied observations of the central supermassive black hole engine of the quasar H1821+643 and possibly get its spin rate. It contains 30 billion times the mass of the Sun. (By comparison, the Milky Way’s central supermassive black hole has only about four billion solar masses.)

Within the Solar System, most of our astrobiological research is aimed at Mars, which is considered to be the next-most habitable body beyond Earth. However, future efforts are aimed at exploring icy satellites in the outer Solar System that could also be habitable (like Europa, Enceladus, Titan, and more). This dichotomy between terrestrial (rocky) planets that orbit within their a system’s Habitable Zones (HZ) and icy moons that orbit farther from their parent stars is expected to inform future extrasolar planet surveys and astrobiology research.

In fact, some believe that exomoons may play a vital role in the habitability of exoplanets and could also be a good place to look for life beyond the Solar System. In a new study, a team of researchers investigated how the orbit of exomoons around their parent bodies could lead to (and place limits on) tidal heating – where gravitational interaction leads to geological activity and heating in the interior. This, in turn, could help exoplanet-hunters and astrobiologists determine which exomoons are more likely to be habitable.

The research was conducted by graduate student Armen Tokadjian and Professor Anthony L. Piro from the University of Southern California (USC) and The Observatories of the Carnegie Institution for Science. The paper that describes their findings (“Tidal Heating of Exomoons in Resonance and Implications for Detection“) recently appeared online and has been submitted for publication in the Astronomical Journal. Their analysis was inspired largely by the presence of multiplanet moon systems in the Solar System, such as those that orbit Jupiter, Saturn, Uranus, and Neptune.

Illustration of Jupiter and the Galilean satellites. Credit: NASA

In many cases, these icy moons are believed to have interior oceans resulting from tidal heating, where gravitational interaction with a larger planet leads to geological action in the interior. This, in turn, allows for liquid oceans to exist due to the presence of hydrothermal vents at at the core-mantle boundary. The heat and chemicals these vents release into the oceans could make these “Ocean Worlds” potentially habitable – something scientists have been hoping to investigate for decades. As Tokadjian explained to Universe Today via email:

Making a 3D map of our galaxy would be easier if some stars behaved long enough to get good distances to them. However, red supergiants are the frisky kids on the block when it comes to pinning down their exact locations. That’s because they appear to dance around, which makes pinpointing their place in space difficult. That wobble is a feature, not a bug of these massive old stars and scientists want to understand why.

So, as with other challenging objects in the galaxy, astronomers have turned to computer models to figure out why. In addition, they are using Gaia mission position measurements to get a handle on why red supergiants appear to dance.

Artist’s impression of the red supergiant star Betelgeuse as it was revealed with ESO’s Very Large Telescope. It shows a boiling surface and material shed by the star as it ages. Credit: ESO/L.Calçada

Understanding Red Supergiants

The population of red supergiants has several common characteristics. These are stars at least eight times the mass of the Sun, and they’re enormous. A typical one is at least 700 to 1,000 times the solar diameter. At 3500 K, they’re much cooler than our ~6000 K star, although measuring those temperatures is tricky. They are super bright in infrared light, but dimmer in visible light than other stars. They also vary in their brightness which (for some of them) may be related to that dancing motion. More on that in a moment.

If the Sun was a red supergiant, Earth wouldn’t be around. That’s because the star’s atmosphere would have reached out to Mars and swallowed our planet up. The best-known examples of these stellar behemoths are Betelgeuse and Antares. Red supergiants exist throughout the galaxy. There’s a population of them you can see at night in a nearby cluster called Chi Persei. It’s part of the well-known “Double Cluster”.

Stars form inside massive clouds of gas and dust called molecular clouds. The Nebular Hypothesis explains how that happens. According to that hypothesis, dense cores inside those clouds of hydrogen collapse due to instability and form stars. The Nebular Hypothesis is much more detailed than that short version, but that’s the basic idea.

The problem is that it only explains how single stars form. But about half of the Milky Way’s stars are binary pairs or multiple stars. The Nebular Hypothesis doesn’t clearly explain how those stars form.

Most stars about the same mass as our Sun or larger aren’t single stars. Most are members of multiple star systems, especially binary stars. While the nebular theory explains how single stars form, there are competing theories for how multiple stars form.

First of all, after a molecular cloud collapses into a star, it forms a rotating disk of gas and dust around the young protostar, called a circumstellar disk. One theory explaining how multiple stars form says that a pair or more of young protostars are fragments of a parent disk that was once much larger. Another theory says that the young protostars form independently, then one captures the other in an orbital arrangement.

But when stars form inside a molecular cloud, it begins with a dense core inside the cloud. That core initiates the gravitational collapse that gathers enough gas in one place to form a star. The question is, what’s different about some of those cores that cause multiple stars to form versus single stars?

Magnetars are some of the most fascinating astronomical objects. One teaspoon of the stuff they are made out of would weigh almost one billion tons, and they have magnetic fields that are hundreds of millions of times more powerful than any magnetic that exists today on Earth. But we don’t know much about how they form. A new paper points to one possible source – mergers of neutron stars.

Neutron stars themselves are equally fascinating in their own right. In fact, magnetars are generally considered to be a specific form of neutron star, with the main difference being the strength of that magnetic field. There are thought to be about a billion neutron stars in the Milky Way, and some of them happen to come in binary pairs.

When they are gravitationally bound to one another, the stars enter a final dance of death, typically resulting in either a black hole or, potentially, one or both of them transforming into a magnetar. That process can take hundreds of millions of years to build up to a certain point when the actual explosion (or collapse) happens. But when it does, it’s spectacular, and a team of researchers thinks they found that that happened only a few weeks before they spotted it.

More accurately, it happened around 228 million years ago, which is how far away the galaxy it happened in is. However, the light from this spectacular event reached the sensors at Pan-STARRs only a few weeks before it started observing that patch of the sky. And what makes this magnetar stand out from all the others scientists have found is how fast it is spinning.

Typically, neutron stars rotate thousands of times per minute, making their period on the order of milliseconds. But the magnetars scientists have found are distinct in that their rotational time is much slower, typically only once every two to ten seconds. But GRB130310A, as the new magnetar is now known, has a rotational period of 80 milliseconds, putting it closer to the order of neutron stars than the typical magnetar.