Astronomer - Blog Posts

Gobble Up These Black (Hole) Friday Deals!

Welcome to our 6th annual annual Black Hole Friday! Check out these black hole deals from the past year as you prepare to head out for a shopping spree or hunker down at home to avoid the crowds.

First things first, black holes have one basic rule: They are so incredibly dense that to escape their surface you’d have to travel faster than light. But light speed is the cosmic speed limit . . . so nothing can escape a black hole’s surface!

Black hole birth announcements

Some black holes form when a very large star dies in a supernova explosion and collapses into a superdense object. This is even more jam-packed than the crowds at your local mall — imagine an object 10 times more massive than the Sun squeezed into a sphere with the diameter of New York City!

Some of these collapsing stars also signal their destruction with a huge burst of gamma rays. Our Fermi Gamma-ray Space Telescope and Neil Gehrels Swift Observatory continuously seek out the signals of these gamma ray bursts — black hole birth announcements that come to us from across the universe.

NICER black holes

There are loads of stellar mass black holes, which are just a few 10s of times the Sun’s mass, in our home galaxy alone — maybe even hundreds of millions of them! Our Neutron Star Interior Composition Explorer, or NICER for short, experiment on the International Space Station has been studying some of those relatively nearby black holes.

Near one black hole called GRS 1915+105, NICER found disk winds — fast streams of gas created by heat or pressure. Scientists are still figuring out some puzzles about these types of wind. Where do they come from, for example? And do they change the way material falls into the black hole? Every new example of these disk winds helps astronomers get closer to answering those questions.

Merging monster black holes

But stellar mass black holes aren’t the only ones out there. At the center of nearly every large galaxy lies a supermassive black hole — one with the mass of millions or billions of Suns smooshed into a region no bigger than our solar system.

There’s still some debate about how these monsters form, but astronomers agree that they certainly can collide and combine when their host galaxies collide and combine. Those black holes will have a lot of gas and dust around them. As that material is pulled into the black hole it will heat up due to friction and other forces, causing it to emit light.  A group of scientists wondered what light it would produce and created this mesmerizing visualization showing that most of the light produced around these two black holes is UV or X-ray light. We can’t see those wavelengths with our own eyes, but many telescopes can. Models like this could help scientists know what to look for to spot a merger.

Black holes power bright gamma ray lights

It also turns out that these supermassive black holes are the source of some of the brightest objects in the gamma ray sky! In a type of galaxy called active galactic nuclei (also called “AGN” for short) the central black hole is surrounded by a disk of gas and dust that’s constantly falling into the black hole.

But not only that, some of those AGN have jets of energetic particles that are shooting out from near the black hole at nearly the speed of light! Scientists are studying these jets to try to understand how black holes — which pull everything in with their huge amounts of gravity — provide the energy needed to propel the particles in these jets. If that jet is pointed directly at us, it can appear super-bright in gamma rays and we call it a blazar. These blazars make up more than half of the sources our Fermi space telescope sees.

Catching particles from near a black hole

Sometimes scientists get a two-for-one kind of deal when they’re looking for black holes. Our colleagues at the IceCube Neutrino Observatory actually caught a particle from a blazar 4 billion light-years away. IceCube lies a mile under the ice in Antarctica and uses the ice itself to detect neutrinos, tiny speedy particles that weigh almost nothing and rarely interact with anything. When IceCube caught a super-high-energy neutrino and traced its origin to a specific area of the sky, they turned to the astronomical community to pinpoint the source.

Our Fermi spacecraft scans the entire sky about every three hours and for months it had observed a blazar producing more gamma rays than usual. Flaring is a common characteristic in blazars, so this didn’t attract special attention. But when the alert from IceCube came through, scientists realized the neutrino and the gamma rays came from the same patch of sky! This method of using two or more kinds of signals to learn about one event or object is called multimessenger astronomy, and it’s helping us learn a lot about the universe.

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10 Things: Mysterious 'Oumuamua

The interstellar object 'Oumuamua perplexed scientists in October 2017 as it whipped past Earth at an unusually high speed. This mysterious visitor is the first object ever seen in our solar system that is known to have originated elsewhere.  Here are five things we know and five things we don’t know about the first confirmed interstellar object to pass through our solar system.

1. We know it’s not from around here.

 The object known as 1I/2017 U1 (and nicknamed ‘Oumuamua) was traveling too fast (196,000 mph, that’s 54 miles per second or 87.3 kilometers per second) to have originated in our solar system. Comets and asteroids from within our solar system move at a slower speed, typically an average of 12 miles per second (19 kilometers per second) . In non-technical terms, 'Oumuamua is an “interstellar vagabond.”

Artist impression of the interstellar object ‘Oumuamua. Credit: ESA/Hubble, NASA, ESO, M. Kornmesser

2. We’re not sure where it came from.

'Oumuamua entered our solar system from the rough direction of the constellation Lyra, but it’s impossible to tell where it originally came from. Thousands of years ago, when 'Oumuamua started to wander from its parent planetary system, the stars were in a different position so it’s impossible to pinpoint its point of origin. It could have been wandering the galaxy for billions of years.

3. We know it’s out of here.

'Oumuamua is headed back out of our solar system and won’t be coming back. It’s rapidly headed in the direction of the constellation Pegasus and will cross the orbit of Neptune in about four years and cover one light year’s distance in about 11,000 years.

4. We don’t really know what it looks like.

We’ve only seen it as a speck of light through a telescope (it is far away and less than half a mile in length), but its unique rotation leads us to believe that it’s elongated like a cigar, about 10 times longer than it is wide. We can’t see it anymore. Artist’s concepts are the best guesses at what it might look like.

5. We know it got a little speed boost.

A rapid response observing campaign allowed us to watch as 'Oumuamua got an unexpected boost in speed. The acceleration slightly changed its course from earlier predictions.

“This additional subtle force on ′Oumuamua likely is caused by jets of gaseous material expelled from its surface,” said Davide Farnocchia of the Center for Near Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory. “This same kind of outgassing affects the motion of many comets in our solar system.”

6. We know it’s tumbling.

Unusual variations in the comet’s brightness suggest it is rotating on more than one axis.

This illustration shows ‘Oumuamua racing toward the outskirts of our solar system. As the complex rotation of the object makes it difficult to determine the exact shape, there are many models of what it could look like. Credits: NASA/ESA/STScI

7. We don’t know what it’s made of.

Comets in our solar system kick off lots of dust and gas when they get close to the Sun, but 'Oumuamua did not, which led observers to consider defining it as an asteroid.

Karen Meech, an astronomer at the University of Hawaii’s Institute of Astronomy, said small dust grains, present on the surface of most comets, may have eroded away during ′Oumuamua's long journey through interstellar space. "The more we study ′Oumuamua, the more exciting it gets." she said. It could be giving off gases that are harder to see than dust, but it’s impossible to know at this point.

8. We knew to expect it.

Just not when. The discovery of an interstellar object has been anticipated for decades. The space between the stars probably has billions and billions of asteroids and comets roaming around independently. Scientists understood that inevitably, some of these small bodies would enter our own solar system. This interstellar visit by ‘Oumuamua reinforces our models of how planetary systems form.

9. We don’t know what it’s doing now.

After January 2018, 'Oumuamua was no longer visible to telescopes, even in space. But scientists continue to analyze the data gathered during the international observing campaign and crack open more mysteries about this unique interstellar visitor.

10. We know there’s a good chance we’ll see another one...eventually.

Because ′Oumuamua is the first interstellar object ever observed in our solar system, researchers caution that it’s difficult to draw general conclusions about this newly-discovered class of celestial bodies. Observations point to the possibility that other star systems regularly eject small comet-like objects and there should be more of them drifting among the stars. Future ground- and space-based surveys could detect more of these interstellar vagabonds, providing a larger sample for scientists to analyze. Adds, Karen Meech, an astronomer at the University of Hawaii’s Institute of Astronomy: “I can hardly wait for the next interstellar object!"

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