NEWS | February 14, 2020

Cosmic Couples and Devastating Breakups

This animation shows what happened in the nine days after a neutron star merger detected in 2017. First, a pair of glowing blue neutron stars spiral quickly toward each other, merging with a bright flash. The merger creates gravitational waves (shown as pale arcs rippling outward), a near-light-speed jet that produced gamma rays (shown as brown cones and a rapidly traveling magenta glow erupting from the center of the collision), and a donut-shaped ring of expanding blue debris around the center of the explosion. A variety of colors represent the wavelengths of light produced by the kilonova, creating violet to blue-white to red bursts above and below the collision.
Doomed neutron stars whirl toward their demise in this illustration. Gravitational waves bleed away orbital energy, causing the stars to move closer together and merge. As they collide, some of the debris blasts away in particle jets moving at nearly the speed of light, producing a brief burst of gamma rays. Credit: NASA’s Goddard Space Flight Center/Conceptual Image Lab

Relationships can be complicated – especially if you’re a pair of stars. Sometimes you start a downward spiral you just can’t get out of, eventually crash together, and set off an explosion that can be seen 130 million light-years away.

Let’s explore the bonds between some of the universe’s notable couples … as well as a few of their cataclysmic endings.

Stellar Couples

When you look at a star in the night sky, you may really be viewing two or more stars dancing around each other. Scientists estimate three or four out of every five Sun-like stars in the Milky Way have at least one partner. Take our old north star Thuban, for example. It’s a binary, or two-star, system in the constellation Draco.

This animation shows two balls glowing in blue-white light orbiting each other. One is about twice the size of the other. The larger ball starts on the left side of the screen and passes in front of the other to the left, then around the back. When the two cross in the middle, they don’t completely cover each other. Trailing behind them as they move are light blue lines indicating the path of their orbits. The animation is watermarked with the text: “Illustration.”
This animation illustrates a preliminary model of the Thuban system, an eclipsing binary system. We view the system at an angle such that they undergo mutual eclipses, but neither is ever completely covered up by its partner. Credit: NASA's Goddard Space Flight Center/Chris Smith (USRA)

Alpha Centauri, our nearest stellar neighbor, is actually a stellar triangle. Two Sun-like stars, Rigil Kentaurus and Toliman, form a pair (called Alpha Centauri AB) that orbit each other about every 80 years. Proxima Centauri is a remote red dwarf star caught in their gravitational pull even though it sits way far away from them (like over 300 times the distance between the Sun and Neptune).

A bright blue-white circle of light dominates this image. It is in the upper left quadrant of the image and appears with a white center that fades out into pale blue hazy edges. This is on a black background awash with small pinpricks of light in colors ranging from blue to pale red. As the animation plays, labels appear. One label identifies the bright star as Alpha Centuari AB. In addition, a circle appears around a small star in the lower right side of the photos that is otherwise indistinguishable from the background stars. This small star is identified as Proxima Centauri. The image is watermarked: “Credit: ESO/Digitized Sky Survey 2/Davide De Martin/Mahdi Zamani.”
This image of the sky around the bright star Alpha Centauri AB also shows the much fainter red dwarf star, Proxima Centauri, the closest star to the solar system. Credit: ESO/Digitized Sky Survey 2/Davide De Martin/Mahdi Zamani

Sometimes, though, a stellar couple ends its relationship in a way that’s really disastrous for one of them. A black widow binary, for example, contains a low-mass star, called a brown dwarf, and a rapidly spinning, superdense stellar corpse called a pulsar. The pulsar generates intense radiation and particle winds that, over millions to billions of years, blow away at all the material of the other star.

A pulsar spins in the middle of this animation with a companion star orbiting around it. The pulsar is represented by a small white dot with two cones of radiation emanating from either side. The cones have a white interior with green outlines closer to the pulsar changing to purple further away. As the animation proceeds, the cones spin around the central pulsar. A sphere representing the pulsar’s companion orbits around the pulsar, and as it does, a continuous cloud of material blows behind it, expanding outward to create a diffuse spiral. The image is watermarked: “Illustration.”
In this illustration of a black widow pulsar from above its orbital plane, gas blown off the companion star trails along its orbit and diffuses throughout the system but is densest along their orbital plane. Credit: NASA's Goddard Space Flight Center/Cruz deWilde

Black Hole Beaus

In romance novels, an air of mystery is essential for any love interest, and black holes are some of the most mysterious phenomena in the universe. They also have very dramatic relationships with other objects around them!

Scientists have observed two types of black holes. Supermassive black holes are hundreds of thousands to billions of times our Sun’s mass. One of these monsters, called Sagittarius A* (the “*” is pronounced “star”), sits at the center of our own Milky Way. In a sense, our galaxy and its black hole are childhood sweethearts – they’ve been together for over 13 billion years! All the Milky-Way-size galaxies we’ve seen so far, including our neighbor Andromeda (pictured below), have supermassive black holes at their center!

The background of this image is dotted with small circles of light in white and shades of pale yellows, reds, or blues. In the center of the image is a large, elongated oval angled from the top left to bottom right with is the disk of the Andromeda galaxy. At the center of the disk is a circle of bright white, with the rest of the disk filled by hazy white. There is also a smaller bright oval above and to the right of the center of Andromeda, which is one of its companion galaxies. The image is watermarked: “Credit: Bill Schoening, Vanessa Harvey/REU program/NOIRLab/NSF/AURA.”
This picture of the Andromeda galaxy and its small companions was made by combining three separate frames derived from photographic plates taken in 1979 at the Burrell Schmidt telescope of the Warner and Swasey Observatory of Case Western Reserve University. Credit: Bill Schoening, Vanessa Harvey/REU program/NOIRLab/NSF/AURA

These black-hole-galaxy power couples sometimes collide with other, similar pairs – kind of like a disastrous double date! We’ve never seen one of these events happen before, but scientists are starting to model them to get an idea of what the resulting fireworks might look like.

Two black holes, shown as black circles, orbit each other in this simulation. Surrounding each black hole is a swirl of gas depicted in shades of bright yellow to hot pink. The gas swirls around the black hole like a pinwheel. As the two orbit, they each leave trails of gas that fades from the hot pink to shades of purple as it forms one large disk surrounding both black holes. The very center of the image is blocked out with a black circle, which is a region that the computer simulations did not model. The image is watermarked: “Simulation.”
Gas glows brightly in this computer simulation of supermassive black holes only 40 orbits from merging. Models like this may eventually help scientists pinpoint real examples of these powerful binary systems. Credit: NASA’s Goddard Space Flight Center

One of the most dramatic and fleeting relationships a supermassive black hole can have is with a star that strays too close. The black hole’s gravitational pull on the unfortunate star causes it to bulge on one side and break apart into a stream of gas, which is called a tidal disruption event.

This animation opens with a starry background and a black circle in the lower right, representing a black hole. From the upper left a small yellow circle enters, representing a small star. The star’s path takes it close to the black circle. It then orbits the black hole, stretching out into a long, thin oval that turns into a stream of patchy gas. One end of the line of gas extends off the screen, dissipating. The other end continues to circle the black hole forming a bright yellow disk. The animation is watermarked: “Illustration.”
When a star approaches the black hole, it can break apart into a stream of gas, as shown in this animation. The tail of the stream escapes the system, while the rest of it swings back around, surrounding the black hole with a disk of debris. Credit: NASA's Goddard Space Flight Center

The other type of black hole you often hear about is stellar-mass black holes, which are a few to hundreds of times the Sun’s mass. Scientists think these are formed when massive stars go supernova. If there are two massive stars in a binary, they can leave behind a pair of black holes that are tied together by their gravity. These new black holes spiral closer and closer until they crash together and create a larger black hole. The National Science Foundation’s LIGO project has detected many of these collisions through ripples in space-time called gravitational waves.

Two black dots circle each other at the center of this animation. Gravitational waves are represented stylistically by spirals that begin as purple, trialing right behind each black hole and then swirling around as they expand off the edge of the screen. The black holes get closer and closer, while the spirals get denser and more frequent until the two black holes merge. As soon as they merge, the new spirals stop, while the existing ones expand away from the single black dot at the center. In the end there is just a single black hole on a black background with a grid, representing space-time.
Two black holes orbit each other, generating space-time ripples called gravitational waves in this animation. As the black holes get closer, the waves increase in until they merge completely. Credit: NASA's Goddard Space Flight Center Conceptual Image Lab

Here’s hoping your relationships are more like a peacefully spiraling stellar binary and less like a tidal disruption! Learn how to have a safe relationship of your own with black holes here.

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