Big Ol’ Black Hole Jets


Some 20,000 light years away, a black hole named GX 339-4 has produced one of the most exciting visible events possible – a massive flare. This searing jet is an extraordinary occurrence and astronomers using NASA’s Wide-field Infrared Survey Explorer (WISE) were able to capture elusive data to further refine their studies of the extreme environments surrounding black holes.

Over the last several decades we’ve learned a lot about these incredible phenomenon, but there’s always room for more. By studying the accretion disk, we know what feeds them and we’ve even seen jet activity through studies using X-rays, gamma rays and radio waves. However, until now, science has never gotten a clear look at the base of jet activity… and it’s exciting more than just the material around it!

“Imagine what it would be like if our Sun were to undergo sudden, random bursts, becoming three times brighter in a matter of hours, and then fading back again. That’s the kind of fury we observed in this jet,” said Poshak Gandhi, a scientist with the Japan Aerospace Exploration Agency (JAXA). He is lead author of a new study on the results appearing in the Astrophysical Journal Letters. “With WISE’s infrared vision, we were able to zoom in on the inner regions near the base of the stellar-mass black hole’s jet for the first time and the physics of jets in action.”

GX 339-4 isn’t particularly unique. It’s about six times solar mass and astronomers have been studying its companion star as the material is being pulled into it. But it’s what’s escaping at nearly the speed of light that’s making researchers sit up and take notice.

“To see bright flaring activity from a black hole you need to be looking at the right place at the right time,” said Peter Eisenhardt, the project scientist for WISE at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif. “WISE snapped sensitive infrared pictures every 11 seconds for a year, covering the whole sky, allowing it to catch this rare event.”

A variable jet? It would seem so. Thanks to NEOWISE, the same area of sky was repeatedly photographed – allowing the team to home in on the elusive base area. Just how elusive? Try to imagine an area the size of your thumbnail seen at the distance of the Sun! Its radius is approximately 15,000 miles (24,140 kilometers) with dramatic changes by as large as a factor of 10 or more. To see an event that lasted anywhere from 11 seconds to a few hours might seem incredulous, but these immense variations blasted through in infra-red.

“If you think of the black hole’s jet as a firehose, then it’s as if we’ve discovered the flow is intermittent and the hose itself is varying wildly in size,” Poshak said.

But that’s not all the data. This new information has given science the best to-date values on black hole magnetic fields – ones that are 30,000 times more powerful than those that belong to planet Earth. It’s these fields that channels the flow of energy and accelerates it. But, there’s still that curiosity factor of why it varies, isn’t there?

We’ll keep asking questions. After all… Science is WISE.

Original Story Source: NASA News.

WISE Discovers Some Really “Cool” Stars!

[/caption]What would you say if I told you there are stars with a temperature close to that of a human body? Before you have me committed, there really is such a thing. These “cool” stars belong to the brown dwarf family and are termed Y dwarfs. For over ten years astronomers have been hunting for these dark little beasties with no success. Now infrared data from NASA’s Wide-field Infrared Survey Explorer (WISE) has turned up six of them – and they’re less than 40 light years away!

“WISE scanned the entire sky for these and other objects, and was able to spot their feeble light with its highly sensitive infrared vision,” said Jon Morse, Astrophysics Division director at NASA Headquarters in Washington. “They are 5,000 times brighter at the longer infrared wavelengths WISE observed from space than those observable from the ground.”

Often referred to as “failed stars”, the Y-class suns are simply too low mass to ignite the fusion process which makes other stars shine in visible light. As they age, they fade away – their only signature is what can be spotted in infrared. The brown dwarfs are of great interest to astronomers because we can gain a better understanding as to stellar natures and how planetary atmospheres form and evolve. Because they are alone in space, it’s much easier to study these Jupiter-like suns… without being blinded by a parent star.

“Brown dwarfs are like planets in some ways, but they are in isolation,” said astronomer Daniel Stern, co-author of the Spitzer paper at JPL. “This makes them exciting for astronomers — they are the perfect laboratories to study bodies with planetary masses.”

The WISE mission has been extremely productive – turning up more than 100 brown dwarf candidates. Scientists are hopeful that even more will emerge as huge amounts of data are processed from the most advanced survey of the sky at infrared wavelengths to date. Just imagine how much information was gathered from January 2010 to February 2011 as the telescope scanned the entire sky about 1.5 times! One of the Y dwarfs, called WISE 1828+2650, is the record holder for the coldest brown dwarf, with an estimated atmospheric temperature cooler than room temperature, or less than about 80 degrees Fahrenheit (25 degrees Celsius).

“The brown dwarfs we were turning up before this discovery were more like the temperature of your oven,” said Davy Kirkpatrick, a WISE science team member at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, Calif. “With the discovery of Y dwarfs, we’ve moved out of the kitchen and into the cooler parts of the house.”

Kirkpatrick is the lead author of a paper appearing in the Astrophysical Journal Supplement Series, describing the 100 confirmed brown dwarfs. Michael Cushing, a WISE team member at NASA’s Jet Propulsion Laboratory in Pasadena, California, is lead author of a paper describing the Y dwarfs in the Astrophysical Journal.

“Finding brown dwarfs near our Sun is like discovering there’s a hidden house on your block that you didn’t know about,” Cushing said. “It’s thrilling to me to know we’ve got neighbors out there yet to be discovered. With WISE, we may even find a brown dwarf closer to us than our closest known star.”

Given the nature of the Y-class stars, positively identifying these special brown dwarfs wasn’t an easy task. For that, the WISE team employed the aid of the Spitzer Space Telescope to refine the hunt. From there the team used the most powerful telescopes on Earth – NASA Infrared Telescope Facility atop Mauna Kea, Hawaii; Caltech’s Palomar Observatory near San Diego; the W.M. Keck Observatory atop Mauna Kea, Hawaii; and the Magellan Telescopes at Las Campanas Observatory, Chile, and others – to look for signs of methane, water and even ammonia. For the very coldest of the new Y dwarfs, the team used NASA’s Hubble Space Telescope. Their final answer came when changes in spectra indicated a low temperature atmosphere – and a Y-class signature.

“WISE is looking everywhere, so the coolest brown dwarfs are going to pop up all around us,” said Peter Eisenhardt, the WISE project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California, and lead author of a recent paper in the Astronomical Journal on the Spitzer discoveries. “We might even find a cool brown dwarf that is closer to us than Proxima Centauri, the closest known star.”

How cool is that?!

Original Story Source: JPL News Release.

How Many Stars are There in the Milky Way?

When you look up into the night sky, it seems like you can see a lot of stars. There are about 2,500 stars visible to the naked eye at any one point in time on the Earth, and 5,800-8,000 total visible stars (i.e. that can be spotted with the aid of binoculars or a telescope). But this is a very tiny fraction of the stars the Milky Way is thought to have!

So the question is, then, exactly how many stars are in the Milky Way Galaxy? Astronomers estimate that there are 100 billion to 400 billion stars contained within our galaxy, though some estimate claim there may be as many as a trillion. The reason for the disparity is because we have a hard time viewing the galaxy, and there’s only so many stars we can be sure are there.

Structure of the Milky Way:

Why can we only see so few of these stars? Well, for starters, our Solar System is located within the disk of the Milky Way, which is a barred spiral galaxy approximately 100,000 light years across. In addition, we are about 30,000 light years from the galactic center, which means there is a lot of distance – and a LOT of stars – between us and the other side of the galaxy.

The Milky Way Galaxy. Astronomer Michael Hart, and cosmologist Frank Tipler propose that extraterrestrials would colonize every available planet. Since they aren't here, they have proposed that extraterrestrials don't exist. Sagan was able to imagine a broader range of possibilities. Credit: NASA
Artist’s impression of the Milky Way Galaxy. Credit: NASA

To complicate matter further, when astronomers look out at all of these stars, even closer ones that are relatively bright can be washed out by the light of brighter stars behind them. And then there are the faint stars that are at a significant distance from us, but which elude conventional detection because their light source is drowned out by brighter stars or star clusters in their vicinity.

The furthest stars that you can see with your naked eye (with a couple of exceptions) are about 1000 light years away. There are quite a few bright stars in the Milky Way, but clouds of dust and gas – especially those that lie at the galactic center – block visible light. This cloud, which appears as a dim glowing band arching across the night sky – is where our galaxy gets the “milky” in its name from.

It is also the reason why we can only really see the stars in our vicinity, and why those on the other side of the galaxy are hidden from us. To put it all in perspective, imagine you are standing in a very large, very crowded room, and are stuck in the far corner. If someone were to ask you, “how many people are there in here?”, you would have a hard time giving them an accurate figure.

Now imagine that someone brings in a smoke machine and begins filling the center of the room with a thick haze. Not only does it become difficult to see clearly more than a few meters in front of you, but objects on the other side of the room are entirely obscured. Basically, your inability to rise above the crowd and count heads means that you are stuck either making guesses, or estimating based on those that you can see.

a mosaic of the images covering the entire sky as observed by the Wide-field Infrared Survey Explorer (WISE), part of its All-Sky Data Release.
A mosaic of the images covering the entire sky as observed by the Wide-field Infrared Survey Explorer (WISE), part of its All-Sky Data Release. Credit: NASA/JPL

Imaging Methods:

Infrared (heat-sensitive) cameras like the Cosmic Background Explorer (aka. COBE) can see through the gas and dust because infrared light travels through it. And there’s also the Spitzer Space Telescope, an infrared space observatory launched by NASA in 2003; the Wide-field Infrared Survey Explorer (WISE), deployed in 2009; and the Herschel Space Observatory, a European Space Agency mission with important NASA participation.

All of these telescopes have been deployed over the past few years for the purpose of examining the universe in the infrared wavelength, so that astronomers will be able to detect stars that might have otherwise gone unnoticed. To give you a sense of what this might look like, check out the infrared image below, which was taken by COBE on Jan. 30th, 2000.

However, given that we still can’t seem them all, astronomers are forced to calculate the likely number of stars in the Milky Way based on a number of observable phenomena. They begin by observing the orbit of stars in the Milky Way’s disk to obtain the orbital velocity and rotational period of the Milky Way itself.


From what they have observed, astronomers have estimated that the galaxy’s rotational period (i.e. how long it takes to complete a single rotation) is apparently 225-250 million years at the position of the Sun. This means that the Milky Way as a whole is moving at a velocity of approximately 600┬ákm per second, with respect to extragalactic frames of reference.

"This dazzling infrared image from NASA's Spitzer Space Telescope shows hundreds of thousands of stars crowded into the swirling core of our spiral Milky Way galaxy. In visible-light pictures, this region cannot be seen at all because dust lying between Earth and the galactic center blocks our view. Credit: NASA/JPL-Caltech
Infrared image of the Milky Way taken by NASA’s Spitzer Space Telescope. Credit: NASA/JPL-Caltech

Then, after determining the mass (and subtracting out the halo of dark matter that makes up over 90% of the mass of the Milky Way), astronomers use surveys of the masses and types of stars in the galaxy to come up with an average mass. From all of this, they have obtained the estimate of 200-400 billion stars, though (as stated already) some believe there’s more.

Someday, our imaging techniques may become sophisticated enough that are able to spot every single star through the dust and particles that permeate our galaxy. Or perhaps will be able to send out space probes that will be able to take pictures of the Milky Way from Galactic north – i.e. the spot directly above the center of the Milky Way.

Until that time, estimates and a great deal of math are our only recourse for knowing exactly how crowded our local neighborhood is!

We have written many great articles on the Milky Way here at Universe Today. For example, here are 10 Facts About the Milky Way, as well as articles that answer other important questions.

These include How Big Is The Milky Way?, What is the Milky Way?, and Why Is Our Galaxy Called the Milky Way?

Astronomy Cast did a podcast all about the Milky Way, and the Students for the Exploration and Development of Space (SEDS) have plenty of information about the Milky Way here.

And if you’re up for counting a few of the stars, check out this mosaic from NASA’s Astronomy Picture of the Day. For a more in-depth explanation on the subject, go to How the Milky Way Galaxy Works.