Category: Astronomy

Seyfert galaxies appear to be normal spiral galaxies, but they have fluctuating bright centers. And now, their deep-down, hidden nature has been revealed: they are cannibals. While visible-light images didn’t provide much evidence that these galaxies had any interaction with their neighbors, radio-telescope images from the Very Large Array revealed that Seyfert galaxies are snacking on neighboring galaxies, with the “meal” feeding the supermassive black hole at their centers. Astronomers had suspected this was the case, but until now, they didn’t have the evidence to support the idea.

One leading theory said that the fluctuations seen in Seyfert galaxies’ centers were caused by close encounters with neighboring galaxies. The gravitational encounters stirred up gas from the neighboring galaxies and brought it within reach of the black hole. However, when astronomers looked at Seyferts with visible-light telescopes, only a small fraction showed any evidence of such an encounter. Now, new images of hydrogen gas in Seyferts made using the National Science Foundation’s Very Large Array (VLA) radio telescope show the majority of them are, in fact, disturbed by ongoing encounters with neighbor galaxies.

“The VLA lifted the veil on what’s really happening with these galaxies,” said Cheng-Yu Kuo, a graduate student at the University of Virginia. “Looking at the gas in these galaxies clearly showed that they are snacking on their neighbors. This is a dramatic contrast with their appearance in visible starlight,” he added.

The effect of the galactic encounters is to send gas and dust toward the black hole and produce energy as the material ultimately is consumed. Black holes, concentrations of matter so dense that not even light can escape their gravitational pull, reside at the cores of many galaxies. Depending on how rapidly the black hole is eating, the galaxy can show a wide range of energetic activity. Seyfert galaxies have the mildest version of this activity, while quasars and blazars are hundreds of times more powerful.

The astronomers picked a number of relatively nearby Seyfert galaxies that had previously been observed with visible-light telescopes. They then carefully studied the Seyferts with the VLA, specifically looking for radio waves emitted by hydrogen atoms. The VLA images showed the vast majority of the Seyferts were disturbed by encounters with neighbor galaxies.

By comparison, similar VLA images of inactive galaxies showed that very few were disturbed. “This comparison clearly shows a connection between close galactic encounters and the black-hole-powered activity in the cores,” said Ya-Wen Tang, who began this work at the Institute of Astronomy & Astrophysics, Academia Sinica (ASIAA), in Taiwan and now is a graduate student at the National Taiwan University.

“This is the best evidence yet for the fueling of Seyfert galaxies. Other mechanisms have been proposed, but they have shown little if any difference between Seyferts and inactive galaxies,” Tang added.

Original News Source: National Radio Astronomy Observatory

Since it was first photographed by the Hubble telescope several years ago, the mystery of Saturn’s aurorae has continued to puzzle scientists. At the beginning, this phenomena only occurred in ultraviolet images, but recent studies done with the ground-based NASA Infrared Telescope Facility show surprising new facets to this colorful display… More than one!

Here on Earth the aurorae occurs when charged particles from the solar wind encounter our magnetic field lines in the upper atmosphere. The particles find their way into Earth’s magnetosphere through “open” field lines located at the north and south pole. These “connect” to the incoming fields associated with the solar wind – like our own personal umbilical cord to the Sun. But we aren’t the only planet to have these dazzling light shows… So does Jupiter.

On our solar system’s largest planet, the charged particles come its volcanic moon – Io. On this inhospitable world, ionized gas is produced and caught up by Jupiter’s fast rotating magnetic field. But this umbilical cord can’t keep up with Jupiter’s dizzying speed at its equator. The thin volcanic gas simply stops co-rotating, slips along Jupiter’s magnetic field lines and pools at giant planet’s polar regions – and the newly discovered second auroral oval glows at Saturn’s co-rotation breakdown latitude, too.

“We’ve been able to find an aurora that seems to be very similar to Jupiter’s,” says Tom Stallard, a planetary astronomer at the University of Leicester in the UK. “At Saturn, only the main auroral oval has previously been observed and there remains much debate over its origin. Here we report the discovery of a secondary oval at Saturn that is 25 per cent as bright as the main oval, and we show this to be caused by interaction with the middle magnetosphere around the planet. This is a weak equivalent of Jupiter’s main oval, its relative dimness being due to the lack of as large a source of ions as Jupiter’s volcanic moon Io.”

So where do the particles come from? We’re not quite sure yet, but accord to Dr. Stallard; “Until relatively recently, it was thought that sputtering off the surface of the icy moons and rings would be the dominant source for Saturn’s plasma.” Stallard also notes that the moon Enceladus and its ice-geyser plume likely provide Saturn’s magnetosphere with about one tenth the material that Io injects into Jupiter’s. This means there is little chance of Saturn’s second aurorae being caused by the same set of circumstances that drives the polar lights on Earth and Jupiter.

For Stallard and his team, the future holds observing the secondary auroras again – looking for variables. But, with Saturn’s equinox now approaching, it may be five or more years until the planet’s north pole points toward us. With a bit of luck, the Cassini Orbiter may be able to help.

New images of Saturn obtained by a University of Colorado at Boulder-led team on June 21 using an instrument on the Cassini spacecraft show auroral emissions at its poles similar to Earth’s Northern Lights. Taken with the Ultraviolet Imaging Spectrograph aboard the Cassini orbiter, the two UV images, invisible to the human eye, are the first from the Cassini-Huygens mission to capture the entire “oval” of the auroral emissions at Saturn’s south pole. They also show similar emissions at Saturn’s north pole, according to CU-Boulder Professor Larry Esposito, principal investigator of the UVIS instrument built at CU-Boulder’s Laboratory for Atmospheric and Space Physics, and Professor Wayne Pryor of Central Arizona College, a UVIS team member and former CU graduate student.

Want to help your kids better understand Jupiter, and the rest of the Solar System?

See Jupiter with your own eyes
The first thing you should do is help them go out and find Jupiter with their own eyes. Jupiter is the third brightest object in the Solar System, after Venus and the Moon – when Jupiter is in the sky, you really can’t miss it. When Jupiter is really well positioned, we’ll have articles here on Universe Today about it.

It’s even better to get your hands on a pair of binoculars, but you won’t be able to see the disk of the planet, or any of its moons without a fairly powerful set of binoculars. Once you look at Jupiter through a telescope, though, it’s easy to see the disk of the planet, bands across its face, and its four largest moons.

Build a scale model of the solar system
Another great project is to build a model of the Solar System. We’ve got instructions here on Universe Today so that you draw a scale model of Sun that fits on a piece of paper, and then how many meters away to put each of the planets, and how big they should be. You can put an entire Solar System within about a kilometer of your house.

Show them what their weight would be on Jupiter
Have your children stand on a scale to see their weight, and then help them see what it would feel like if they were standing on the surface of Jupiter (of course, Jupiter doesn’t actually have a surface). Then push down on their shoulders and have the scale increase in weight. Your weight on Jupiter is 2.5 times your weight on Earth. Don’t push too hard, they’ll probably tell you it’s too much pretty quickly. The stand with them on the scale, and even that probably won’t be enough.

Draw Jupiter
Get out your crayons and try drawing Jupiter. The dark colored stripes on Jupiter are called bands, and the light colored stripes are zones, and they alternate across the surface of Jupiter. You’ll also want to include the Great Red Spot, and maybe Red Spot Jr. The smaller storms are brown or yellow, and the smallest ones are white.

Here’s a link to the project that explains how to build a model of the Solar System, and here are some images of Jupiter you can use when drawing your own version.

Kids Astronomy has more projects you can do with your kids, and an astronomer answers questions about Jupiter.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

Reference:
NASA

I’m lucky enough to have twin sons. They aren’t identical (one looks like me, the other looks like my husband – which is about as different as things get) but they have a lot of similarities. One of my favorite stories about having twins is the time we took the whole family out to a restaurant shortly after the twins were born. The waitress commented that our babies looked the same size, and we said, “Yes, they’re twins.” And she replied, “Oh really? How far apart in age are they?”

I used to think that waitress was a real ditz, but after seeing a press release today from Vanderbilt University, I’m wondering if the waitress was on to something, and maybe she was even an astronomer.

Astronomers recently found a very young pair of identical binary stars that have surprising differences in brightness, surface temperature and size. They also believe one of the stars formed significantly earlier than its twin. Astrophysicists have assumed that binary stars form simultaneously, and so this discovery forces theorists back to the drawing board to determine if their models can produce binaries with stars that form at different times.

The identical twins were discovered in the Orion Nebula, a well-known stellar nursery, 1,500 light years from Earth. The newly formed stars are about 1 million years old. With a full lifespan of about 50 billion years, that makes them equivalent to one-day-old human babies.

“Very young eclipsing binaries like this are the Rosetta stones that tell us about the life history of newly formed stars,” says Keivan Stassun, associate professor of astronomy at Vanderbilt University. He and Robert D. Mathieu from the University of Wisconsin-Madison headed up the project.

The astronomers calculated that these twin stars have nearly identical masses, about 41 percent that of the sun. According to current theories, mass and composition are the two factors that determine a star’s physical characteristics and dictate its entire life cycle. Because the two stars condensed from the same cloud of gas and dust they should have the same composition. And with identical mass and composition, they should be identical in every way. So the astronomers were surprised when they discovered that the twins exhibited significant differences in brightness, surface temperature and possibly size.

“The easiest way to explain these differences is if one star was formed about 500,000 years before its twin,” says Stassun. “That is equivalent to a human birth-order difference of about half of a day.”

Now, I have heard stories of twins being born several hours apart and even in different years (one late on Dec. 31, and the other early on Jan. 1) so, maybe this difference in star formation isn’t such a big deal, and it happens all the time. However, further study is needed.

But this new discovery may cause astronomers to readjust their estimates of the masses and ages of thousands of young stars less than a few million years old, as current estimates are based on models that presumed binary stars formed simultaneously.

Just like having twins causes you to readjust your entire life. But it’s a good readjustment.

Original News Source: Vanderbilt University (this link includes a nice multimedia presentation about the discovery)

Worried about how you’re going to feed your black hole once it grows up and gets big? Have no fear. New data from the Chandra X-ray Observatory indicates that even the biggest black holes may feed just like the smallest ones. Using new observations and a detailed theoretical model, a research team compared the properties of the black hole of the spiral galaxy M81 with those of smaller, stellar mass black holes. The results show that big or little, black holes appear to eat similarly to each other, and produce a similar distribution of X-rays, optical and radio light. This discovery supports the implication of Einstein’s relativity theory that black holes of all sizes have similar properties.

M81 is about 12 million light years from Earth. In the center of M81 is a black hole that is about 70 million times more massive than the Sun, and generates energy and radiation as it pulls gas in the central region of the galaxy inwards at high speed.

In contrast, so-called stellar mass black holes, which have about 10 times more mass than the Sun, have a different source of food. These smaller black holes acquire new material by pulling gas from an orbiting companion star. Because the bigger and smaller black holes are found in different environments with different sources of material to feed from, a question has remained about whether they feed in the same way.

“When we look at the data, it turns out that our model works just as well for the giant black hole in M81 as it does for the smaller guys,” said Michael Nowak, from the Massachusetts Institute of Technology. “Everything around this huge black hole looks just the same except it’s almost 10 million times bigger.”

One of the implications of Einstein’s theory of General Relativity is that black holes are simple objects and only their masses and spins determine their effect on space-time. The latest research indicates that this simplicity manifests itself in spite of complicated environmental effects.

The model that Markoff and her colleagues used to study the black holes includes a faint disk of material spinning around the black hole. This structure would mainly produce X-rays and optical light. A region of hot gas around the black hole would be seen largely in ultraviolet and X-ray light. A large contribution to both the radio and X-ray light comes from jets generated by the black hole. Multi-wavelength data is needed to disentangle these overlapping sources of light.

Among actively feeding black holes the one in M81 is one of the dimmest, presumably because it is “underfed”. It is, however, one of the brightest as seen from Earth because of its relative proximity, allowing high quality observations to be made.

“It seems like the underfed black holes are the simplest in practice, perhaps because we can see closer to the black hole,” said Andrew Young of the University of Bristol in England. “They don’t seem to care too much where they get their food from.”
This work should be useful for predicting the properties of a third, unconfirmed class called intermediate mass black holes, with masses lying between those of stellar and supermassive black holes. Some possible members of this class have been identified, but the evidence is controversial, so specific predictions for the properties of these black holes should be very helpful.

In addition to Chandra, three radio arrays (the Giant Meterwave Radio Telescope, the Very Large Array and the Very Long Baseline Array), two millimeter telescopes (the Plateau de Bure Interferometer and the Submillimeter Array), and Lick Observatory in the optical were used to monitor M81.
The results of this study will appear in an upcoming issue of The Astrophysical Journal.

News Source: NASA’s Chandra Website