Black holes, ranked

They don't have a surface, like a planet or a star. They're only visible when their shadows creep across something bright in the sky. And, if that weren't unsettling enough, they serve as galactic pool drains, sucking celestial material that comes too close toward a point of no return.

Black holes: not your everyday death traps.

During a star's death, an enormous amount of solar material collapses onto itself, packing tightly into a small space. How much material? Sometimes millions to billions of times the mass of the sun compressed into an area only measuring a few miles across. The gravitational pull of a black hole is so strong, nothing — not even light — can escape.

But when it comes to invisible space objects, it's tough to compare one to another.

No worries: Mashable has developed a rating system (proprietary) that scores black holes based on mass, spin, location, orbiting companions, historical significance, and flair — not to be mistaken for flare, as in the flares of X-rays that can sometimes rapidly shoot out. When we say "flair," we mean each hole's unique je ne sais quois.

10. The neighbor

Sagittarius A* is the supermassive black hole found in the center of the Milky Way galaxy. Credit: NASA/University of Delaware/Catholic University of America/Christopher Russell

Meet your neighborhood black hole, Sagittarius A*. This is the supermassive black hole at the heart of the Milky Way.

But it's not as close as you might think. Scientists have estimated its distance at 26,000 light years from Earth. The black hole is also 4 million times the mass of the sun. If you're wondering what exactly the mass of the sun is, let's put it this way: Take Earth, then multiply it 333,000 times.

The hole's accretion disk, that ring of gas and dust swiveling around it, is surprisingly not that bright. Unlike any other known black hole, the disk sends out flickering flares every hour, making it scientifically interesting.

Sagittarius A* is also the Violet Beauregarde of black holes. Like the gum-chewing character who took a tour of Willy Wonka's factory, this black hole is forever blowing bubbles—specifically, two enormous bubble-like structures full of cosmic rays, one above and one below the galaxy, according to a new study.

9. The first

Stephen Hawking famously lost a bet, placed in 1974, over whether Cygnus X-1 contained a black hole. Credit: Optical: DSS; Illustration: NASA/CXC/M.Weiss Press Image and Caption

Cygnus X-1 is the black hole that started it all.

Though it was discovered in 1964 as a source of mysterious X-rays, the scientific community didn't agree it was a black hole for another three decades.

Stephen Hawking famously lost a bet, placed in 1974, over whether Cygnus X-1 included a black hole, and Hawking's concession in 1990 that he was wrong was a milestone for the study of these elusive regions in spacetime. Now it's one of the most studied objects in space, with scientists learning new information about it even today.

Cygnus X-1 feeds on a blue companion star and is 21 times the mass of the sun.

8. The tilted one

The black hole system MAXI J1820+070 is tilted more than 40 degrees from the system's orbital axis. Credit: Image produced with Binsim/ R. Hynes

This one spins on its side.

Researchers found a system composed of a collapsed massive star pulling matter away from a companion star — in other words a black hole and white dwarf orbiting tightly around one another. Called MAXI J1820+070, the duo is located in the Milky Way about 10,000 light years from Earth. To make matters weirder, the black hole's tilt and its orbit are on totally different axes.

The fact that this tilted black hole exists challenges theories on how holes form. Just how tilted is it? Astronomers measured the orbital axis of the system and compared it to information known about the black hole's spin. The data revealed the rotation axis was tilted more than 40 degrees from the system's orbital axis.

7. The soon-to-be colliding

A pair of black holes in PKS 2131-021 gets closer to merging. Credit: Caltech-IPAC

A supermassive black hole 9 billion light years away appears to have a giant buddy that's getting a little too close for comfort.

As the orbit shrinks, the pair of black holes in the PKS 2131-021 galaxy gets ever closer to colliding. This is only the second pair of black holes observed on the verge of merging.

It took 45 years of radio data to come to this conclusion, said Joseph Lazio of NASA’s Jet Propulsion Laboratory in Southern California in a statement. The two black holes circle one another every two years.

The impact is expected to happen in about 10,000 years. That might seem like a long time from now, but it would take 100 million years for black holes of this size to begin orbiting and then merge. NASA said these two are more than 99 percent of the way to their big crash.

6. The shredder

When a star comes too close to a black hole, like the one here in the PGC 043234 galaxy, its gravity causes tidal forces that can rip the star into shreds. Credit: NASA/CXC/U. Michigan/J. Miller et al.; Illustration: NASA/CXC/M. Weiss

Scientists caught a black hole at the center of a galaxy 290 million light years from Earth in the middle of a gruesome feast.

When a star comes too close to a black hole, like the one here in the PGC 043234 galaxy, its gravity causes tidal forces that can rip the star into shreds. In these events, some of the stellar debris is hurled out at high speeds, while the rest falls into the black hole. This causes a distinct X-ray flare that can last for years.

With three X-ray telescopes, a team of astronomers detected the last "cry" from a star that passed too close to the black hole and was being devoured.

“The black hole tears the star apart and starts swallowing material really quickly, but that’s not the end of the story,” said Jelle Kaastra, one of the study's authors from the Institute for Space Research in the Netherlands. “The black hole can’t keep up that pace so it expels some of the material outwards.”

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5. The middleweight

The black hole in B023-G078 is one of the only confirmed intermediate-mass black holes. Credit: Iván Éder, HST ACS/HRC

This black hole is special for being in the middle, so the only fitting rank for it is right here at the middle of our list.

The black hole is within B023-G078, a giant star cluster in the galaxy next door to us, Andromeda.

At 100,000 solar masses, it is smaller than the black holes found at the centers of most galaxies, but bigger than the black holes born when stars bust. This makes it one of the only confirmed intermediate-mass black holes, according to a study published in The Astrophysical Journal in January.

The new black hole is what’s known as a “stripped nucleus,” composed of remnants of small galaxies that have fallen into bigger ones, with their outer stars stripped away by gravitational forces. What's left is a seriously tiny and dense nucleus of what was at one time a small galaxy orbiting a bigger galaxy, which also has a black hole at its center.

4. The thriller

What makes GRS 1915+105 unusual is that it's spinning about 1,000 times per second. Credit: X-ray (NASA/CXC/Harvard/J.Neilsen et al); Optical (Palomar DSS2)

GRS 1915+105, which involves two stars, is the mother of all Teacups rides. The system is based in the Aquila constellation about 35,000 light years from Earth, and contains a black hole about 14 times the sun's mass.

Like in all black holes, star gases swirl toward the center, sucked into a whirlpool by gravity. As they spiral, they form a reservoir of material around the hole called an accretion disk.

What makes GRS 1915+105 unusual is that it's spinning about 1,000 times per second. That's the maximum possible rate. Scientists measure the spin to determine how strongly the black hole drags spacetime right outside the hole's event horizon, the point beyond which nothing can escape.

3. The missing link

Scientists are calling GNz7q a crucial "missing link" between young galaxies just beginning to form stars and quasars. Credit: NASA, ESA, Garth Illingworth (UC Santa Cruz), Pascal Oesch (UC Santa Cruz, Yale), Rychard Bouwens (LEI), I. Labbe (LEI), Cosmic Dawn Center/Niels Bohr Institute/University of Copenhagen, Denmark

This discovery came in just under the wire this April to make this list. Scientists are calling GNz7q a crucial "missing link" between young galaxies just beginning to form stars and quasars, luminous objects in the early universe.

Current theories predict that supermassive black holes like this one begin their lives in the dust-shrouded cores of starburst galaxies before evolving into quasars.

"GNz7q provides a direct connection between these two rare populations and provides a new avenue toward understanding the rapid growth of supermassive black holes in the early days of the universe," said Seiji Fujimoto, an astronomer at the Niels Bohr Institute of the University of Copenhagen and lead author of the study, in a statement. "Our discovery provides an example of precursors to the supermassive black holes we observe at later epochs."

Scientists believe this black hole existed just 750 million years after the Big Bang.

The mixture of radiation coming from the object can't be attributed to star formation alone, according to NASA. The source of ultraviolet and infrared light is consistent with the materials expected to fall onto a black hole.

2. The star reincarnate

Rather than ripping stars to shreds and swallowing up every morsel, this black hole in Henize 2-10 is fostering star formation in a dwarf galaxy. Credit: NASA, ESA, Z. Schutte (XGI), A. Reines (XGI), A. Pagan (STScI)

Black holes are poorly understood cosmic bodies, generally thought of as mere vacuums sucking light out of the universe.

A black hole in Henize 2-10 actually takes that negative stereotype and turns it on its head. Rather than ripping stars to shreds and swallowing up every morsel, this black hole is fostering star formation in a dwarf galaxy. It's like reincarnation.

Hubble Space Telescope imaging and spectroscopy show a gas stream stretching from the black hole to a bright star birth region "like an umbilical cord," according to NASA, triggering the formation of clusters of stars.

The photo above shows the galaxy glittering with young stars. The bright center, wreathed in pink clouds and dark dust, indicates the site of the black hole.

1. The proof

M87's black hole is the first ever photographed. What you're seeing is its shadow cast on the bright accretion disk circling it. Credit: Event Horizon Telescope collaboration et al.

More than 55 million light years from Earth lies a special supermassive black hole. This hole, located at the center of the elliptical galaxy Messier-87, has a mass 6.5 billion times that of the sun.

But that's not what makes it exceptional. What makes M87 deserving of the No. 1 slot? Simple: We have photographic evidence of it.

Black holes are by definition invisible — no light can travel fast enough to escape them. Astronomers detect them from the way their gravity interacts with other objects, and artists create dramatic illustrations and videos to depict them.

In this case, scientists snapped M87's black hole in silhouette. They accomplished this feat with eight ground-based radio telescopes working together as one telescope the size of Earth.