Posts Tagged ‘galaxy’

Ghosts Lurking from Massive Black Hole

Thursday, June 4th, 2009 by Bellatrix

We all know that super massive black holes lurk in the center of galaxies. We know that they can have strong impacts on the surroundings; usually we can see how things are being impacted by the outflows of energetic particles being ejected from feeding black holes. However, if a black hole is not active and does not have jets usually we cannot see anything left over, any remnants from its energetic past. Well recently using the Chandra X-ray observatory a ghost of an eruption from a massive black hole has been observed and may have some interesting things to tell us.

The X-ray ghost, so-called because a diffuse X-ray source has remained after other radiation from the outburst has died away, is in the Chandra Deep Field-North, one of the deepest X-ray images ever taken. The source HDF 130 is over 10 billion light-years away a time when galaxies and black holes were forming at a high rate. Scientists think the X-ray glow from HDF 130 is evidence for a powerful outburst from its central black hole in the form of jets of energetic particles traveling at almost the speed of light. When the eruption was ongoing, it produced large amounts of radio and X radiation, but after several million years, the radio signal faded from view as the electrons radiated away their energy.

However, less energetic electrons can still produce X-rays by interacting with the pervasive sea of photons remaining from the cosmic background radiation. Collisions between these electrons and the background photons can impart enough energy to the photons to boost them into the X-ray energy band. This process produces an extended X-ray source that lasts for another 30 million years or so.

This is the first X-ray ghost ever seen after the demise of radio-bright jets. Astronomers have observed extensive X-ray emission with a similar origin, but only from galaxies with radio emission on large scales, signifying continued eruptions. In HDF 130, only a point source is detected in radio images, coinciding with the massive elliptical galaxy seen in its optical image. This radio source indicates the presence of a growing supermassive black hole.

The power contained in the black hole eruption was likely to be considerable, equivalent to about a billion supernovas. The energy is dumped into the surroundings and transports and heats the gas. Because they’re so powerful, these eruptions can have profound effects lasting for billions of years.

The data tells us that there should be many more such ghosts lurking around out there, especially if black hole eruptions are as common as are thought in the distant universe. This is a good discovery as it tells us that we do not have to catch a black hole in the act to witness the big impact they can have. Using Chandra I’m sure searches will begin for other such remnants. Once we have found more of them we can search for patterns in the data, see if there are commonalities in these eruptions or links between the data and other such things such as the mass of the black hole. 

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Microquasars: Black Holes and Normal Stars an Interesting Mix

Tuesday, December 2nd, 2008 by Bellatrix

Astronomers using two different telescopes and two different systems have started learning about microquasars. They’re learning new things that can then hopefully be applied to full size quasars as well.

A quasar is an extremely powerful, luminous and distant active galactic nucleus. While there was initially some controversy over the nature of these objects, there is now a scientific consensus that a quasar is a compact region surrounding the central supermassive black hole of a galaxy. Quasars show a very high redshift, meaning they are located a great distance from us. Quasars are active because the central black hole is accreting a lot of material. Near the black hole, intense magnetic fields in the disk accelerate material into tight jets that flow in opposite directions away from the hole.

Microquasars is a two-body system consisting of a stellar mass size black hole and a star, usually a red giant. The giant star is feeding material to the black hole. Which, needless to say creates some interesting dynamics. Astronomers have been looking at two systems, Swift1753.3-0127 and GX339-4, with the European Southern Observatory’s Very Large Telescope and NASA’s Rossi X-ray Timing Explorer to study microquasars. Microquasars are not only closer but change more rapidly, so a process that may take a normal quasar a year to undergo might only take a microquasar a few minutes.

Astronomers had thought that the visible light emission coming form microquasars was coming form far out in the accretion disk and thus did not give much information about the main actions going on. However, they were wrong. They now know that the optical and x-ray emission are intrinsically linked, probably by the same immense magnetic fields that hurl material into near light speed jets.

The data shows that light output typically drops just before x-ray output undergoes a large spike. The rapid variations in the x-ray and optical emission must have a common origin. The cool thing about discovering such patterns that stand out amidst chaotic fluctuations of light is that they give us a new handle on understanding the underlying physics. The best candidate is the strong magnetic fields as the dominant process behind it all.

So again what we once thought was wrong, we learned something new, but realize how much we don’t know yet. This data is a new clue about very mysterious and not yet understood systems. We still don’t know exactly what’s going on in these dynamic systems, but we have one more piece of the puzzle.

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Double Checking Our Data

Wednesday, November 26th, 2008 by Bellatrix

Scientists believe they have found the answer to a mystery about a thought to be nearby galaxy. The funny thing is this answer was found by rather serendipitously after finding out our current estimates for the distance of the galaxy were wrong.

The galaxy named NGC 1569 was a bit of a mystery. It is an irregular shaped dwarf galaxy, which isn’t in itself strange, but the galaxy was going through a burst of star formation with no discernable reason. The galaxy was forming stars much faster than any other galaxies in its nearby region. Well then we realized that the problem with that statement was not NGC 1569 itself but the galaxies we thought were nearby it.

Scientists recently pointed the Hubble Space telescope at NGC 1569 to scan for red giant stars. The astronomers were hoping to get an estimate of the galaxies age by looking for red giants, as red giants can be used as reliable standard candles for measuring distance since they all burn at the same known brightness. However, the astronomers were only able to see the brightest red giants, even using Hubble, the stars were too dim to be resolved. This fact lead astronomers to question the previous estimate for how far away the galaxy actually is. And now after looking at the data astronomers have realized the galaxy is actually about one and a half times farther away than previously thought, making it about 11 million light years away.

The problem was before this the galaxy had only been studied with ground based telescopes, which have much less resolving power than space based telescopes, which can make estimates less accurate. With this new information the galaxy’s star formation makes more sense. This distance puts the galaxy in the middle of a cluster of ten other galaxies. The gravitational interaction of the galaxies tugging on each other would be enough to explain the high rate of star formation we see in this galaxy.

So using Hubble we have answered yet another question, good ol’Hubble. However, this instance makes one wonder how many other numbers that we have for things like distance or mass etc might be inaccurate after only being studied by ground-based telescopes. How many things should we go back over with space-based telescopes to make sure? And how many mysteries or unexplainable phenomena might be answered by simply rechecking our data??

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Galaxy Having a Major Baby Boom

Monday, October 27th, 2008 by Bellatrix

Astronomers have discovered a distant galaxy making stars at an amazing rate. It is creating stars at a rate more than a thousand times that of the Milky Way, but the remarkable thing about it is its extreme distance. This galaxy may call into question the current theory of how galaxies form.

The galaxy, nicknamed the baby boom galaxy, is making stars at a rate of about 4000 per year, compared to the Milky Way, which makes only 10 stars per year. This galaxy is also located very far from us, 12.3 billion light years. We have observed other starburst galaxies before, but none this far away, or similarly this old. This galaxy is a very young galaxy, since it is so far, we are looking at it as it was almost 12 billions years ago. That gives this galaxy the record for furthest (or youngest) starburst galaxy ever observed. The furthest before this one was 11.7 billion light years from us.

Now this galaxy calls into question the current most popular model for how galaxies are believed to form, called the hierarchal model. This model states that galaxies form slowly by consuming other smaller galaxies and star clusters, thus the stars in the galaxies should all have different birthdays. However, with this new galaxy all the stars will have very similar birthdays, meaning formation of around the same time. So the question now is whether this case is the norm or the exception. With this kind of star formation we may be witnessing the birth of one of the most massive elliptical galaxies in the universe.

The discovery of this was only possible through combined use of several different telescopes. Measurements in the radio wavelengths were made with the National Science Foundation’s Very Large Array in New Mexico. Infrared data was used from both the Spitzer space telescope and the James Clerk Maxwell Telescope on Mauna Kea Hawaii. Visible light images were used from both the Hubble Space Telescope and Japan’s Subaru Telescope also atop Mauna Kea. The identification of this galaxy and its properties would not have been possible without observations in the full range of the light spectrum. So its discovery is a fine example of the combination of different available technologies, from different sponsoring organizations. Now that we know how to find them, i.e. using data from across the electromagnetic spectrum, hopefully we can find out if galaxy baby booms were common in the distant universe, and if not, what is special about this case.

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