We tend to think of these scary objects as having voracious appetites, gobbling up everything that gets in their way. But in reality, most black holes surround themselves with discs of gas and dust that swirl around, heat up, and emit lots of radiation. All this activity makes it difficult to determine what’s going on near the black hole itself. Which includes figuring out the black hole’s diet.

If we want to understand something that’s invisible (such as a black hole), we usually have to find creative ways of detecting it. But in order to learn about the black hole at the center of our galaxy, astronomers study the behavior of its surroundings—specifically nearby stars.

They hit the jackpot once they discovered a pulsar near the galactic center. Not only do these rare stars act as precise cosmic clocks, but this one in particular emits an abnormally strong magnetic field (called a magnetar).

Pulsar PSR J1745-2900 was the first of its kind to be found near the galactic center, and at only 0.3 light years away from our black hole (a.k.a. Sagittarius A* or Sgr A*), it tells us a lot about black hole characteristics.

A research team with the Max Planck Institute for Radio Astronomy (MPIfR) was able to measure the pulsar’s magnetic field, which revealed how magnetic fields affect black hole behavior.

“In order to understand the properties of Sgr A*, we need to comprehend the accretion of gas into the black hole,” says Michael Kramer, director at MPIfR. Although black holes have infamously strong gravity, material doesn’t typically fall directly into a black hole; instead, the material forms an accretion disc before slowly flowing toward the black hole at the center.

“However, up to now,” according to Kramer, “the magnetization of the gas, which is a crucial parameter determining the structure of the accretion flow, remains unknown. Our study changes that by using the discovered pulsar to probe the strength of the magnetic field at the start of this accretion flow of gas into the central object.”

Knowledge of pulsars’ consistent frequencies illustrates the effect of the black hole on the pulsar. Radio waves usually polarized along a plane are now rotating in a corkscrew motion, similar to the radiation emitted from black holes themselves.

“The rotation is way higher than anything seen in the Galaxy with the exception of Sagittarius A*,” says Ralph Eatough of MPIfR who measures the black hole’s radio waves and outward streaming matter.

The paper, published last week in Nature, concludes that the twisted magnetic fields might slow black holes’ diet, putting the brakes on infalling gas. Sgr A* is “not feeding to its full potential,” says Eatough.

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image: NASA

Black holes seem to pique everyone’s interest. From the first theories to the first (indirect) observations, pretty much everyone has wanted to know more.

Unfortunately, black holes have remained notoriously tight-lipped with their secrets; by definition, these objects are so massive and compact that light itself cannot escape their gravitational influence, which makes studying them directly almost impossible.

Most of what we know about black holes has been inferred from their influence on the objects around them, such as the incredibly fast stars that orbit the supermassive black hole in the center of our galaxy (a relatively lightweight juggernaut that weighs in at merely millions of times the mass of the Sun). Other galaxies may have similar black holes within them, but this has been speculation until now.

In a recent paper from Tim Davis, of the University of Hertfordshire, scientists can observe the carbon dioxide clouds in the center of some galaxies to measure (again indirectly, but with great precision) the mass of black holes contained within. By watching the carbon dioxide molecules “circling the drain” these scientist have developed a new way to determine the mass of very distant black holes, ones so far away that there was no hope of ever seeing individual stars in orbit around them.

These distant galaxies are important to scientists for a number of reasons, but perhaps the biggest is that since they lie so far away, light takes millions or billions of years to span that distance. The further away a galaxy, the further “back in time” we see it! By observing these distant galaxies, scientist are hoping to determine the role these supermassive black holes play in the formation of galaxies and perhaps better understand our own galaxy’s evolution and how we came to be within it.

Josh Roberts is a program presenter and astronomer at the California Academy of Sciences. He also contributes content to Morrison Planetarium productions.

Image courtesy of University of Hertfordshire

As Einstein might say, speed is relative. It certainly captures our imagination. For example, you may think you’re sitting still, but by some reckoning, you are moving incredibly fast—as Earth spins and orbits within the Solar System and as the Sun makes its way around the Milky Way. In fact, for us to make a full rotation around the galactic center every 250 million years, we have to be moving at the brisk pace of half a million miles an hour!

But as fast as we are moving, it’s a leisurely stroll compared to some stars that have made recent headlines. These so called “hypervelocity stars” are allowing scientists a first hand view of the incredible and mysterious super-massive black hole at the center of our Milky Way galaxy. Since we cannot observe the black hole directly, we study the motion of nearby matter—stars, gas, and dust—to learn much about the black hole’s mass and how it distorts space around it. These observations grant astrophysicists an opportunity to test the inner workings of Einstein’s theory of relativity on a grand scale.

Another group of super-fast superstars out there seems to be related. They are not gravitationally bound to the black hole, or anything else in the galaxy. In fact, they have been flung out from the Milky Way at speeds so great that they will actually escape it entirely! Some scientists have speculated that these “runaway” or “rogue” stars may have once been the companions of the very same hypervelocity stars that orbit within the Milky Way, but these rogue stars were flung off long ago when their partners were pulled into the supermassive black hole’s gravitational influence.

Another possible origin for the stellar speedsters could be a companion or nearby star that went supernova and blasted them out into the great beyond. Astronomers search for these stars before they exit the galaxy by looking for the tell-tale bow shock they create as they pass through the thin gas of the Milky Way, much like the wake a speedboat creates on a calm lake.

No matter their origins, hypervelocity stars and any other super speedy things provide critical windows into relativity and the nature of space and time. Special relativity predicts the ways in which physics will change as something approaches the speed of light; general relativity describes the behavior of objects in intense gravitational fields (like you might find near a black hole, hmm…). These stars and others like them give us a great chance to challenge our ideas about the nature and workings of our universe and get a view “beneath the hood” to understand how it has changed and evolved over time.

Josh Roberts is a program presenter and astronomer at the California Academy of Sciences. He also contributes content to Morrison Planetarium productions.

Image: Ethan Tweedie

(The swiss cheese analogy is courtesy of Brian Greene from a Radiolab episode from 2008. Go ahead, let your mind be further blown and listen to the whole thing.)

In today’s edition of Physics Letters B, theoretical physicist Nikodem Poplawski of Indiana University suggests that our universe could be located within the interior of a wormhole which itself is part of a black hole that lies within a much larger universe.

Huh?

A wormhole is a shortcut through spacetime (and also what Jodie Foster travels through near the end of the movie Contact). So Universe Today puts it this way, “A wormhole is a hypothetical ‘tunnel’ connecting two different points in spacetime, and in theory, at each end of the wormhole there could be two universes.”

One headline about this research compares these universes to Russian nesting dolls. The paper suggests that all black holes may have wormholes, each with a new universe inside that formed simultaneously with the black hole. According to Poplawski, “From that it follows that our universe could have itself formed from inside a black hole existing inside another universe.”

Got it?

It’s very a cool, mind-blowing theory. And the trick with any multiverse theory, according to a great New Scientist article last month, is that while it may be probable, it is essentially untestable. Unless you pull a Jodie Foster and travel through the wormhole yourself. Bon voyage.

Creative Commons image by AllenMcC