Astronomy

What is this bright “glow” in the center of galaxies?

What is this bright “glow” in the center of galaxies?


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It was always my belief that at the center of many galaxies, there are supermassive black holes. If this is the case, then we should not see a "light" coming out from the center since light get's sucked in black holes. Doing a quick search of galaxies on google image, I came across this:

These are famous galaxies, and real, and so I was wondering what this very white-yellow glow is in the center. If it is a collection of stars, then why are there so many stars in the center of a galaxy? If there is a black hole there, then why is there light?


If this is the case, then we should not see a "light" coming out from the center since light get's sucked in black holes.

You are overestimating the size and the capabilities of a supermassive black hole. Contrary to pop sci portrayals of black holes, black holes are not giant vacuum cleaners in space that suck up anything and everything close by. While the supermassive black hole at the center of the Milky Way is indeed very massive (about four million times the mass of our Sun), it isn't very large physically. It's less than a couple dozen solar diameters across. It also isn't that hungry, gobbling up perhaps the equivalent of four or so Earth masses over the course of a year.

On the other hand, the central bulge of a spiral galaxy contains several million stars in a fairly small volume. That central bulge is what you are seeing in those images. The supermassive black holes near the centers of those bulges gobbles only a tiny, tiny fraction of the light emitted by those millions of stars.


Remember that there are millions of stars in that central hub between the black hole and us. We are seeing their light. The fact that there is a black hole behind them is not relevant.


Seyfert galaxy

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Seyfert galaxy, any of a class of galaxies known to have active nuclei. Such galaxies were named for the American astronomer Carl K. Seyfert, who first called attention to them in 1944. Two types are recognized. The nuclear spectra of Type 1 Seyfert galaxies show broad emission lines, which are indicative of a central concentration of hot gas that is expanding at speeds of up to thousands of kilometres per second. Type 2 Seyferts have strong emission lines, but they indicate more-modest velocities, less than 1,000 km/sec. Seyfert galaxies appear normal in ordinary images but are extremely strong sources of infrared radiation. Moreover, many are powerful sources of radio energy and X-rays as well. Seyfert nuclei are related to quasars but apparently involve smaller amounts of energy release. Like quasars, they are thought to be powered by massive black holes at their centres. About 1 percent of all spiral galaxies are thought to exhibit Seyfert properties, or perhaps all spiral galaxies are Seyferts 1 percent of the time.


What is this bright &ldquoglow&rdquo in the center of galaxies? - Astronomy

The galactic bulge is the bright bulge in the center. The Chandra X-Ray Observatory is able to pierce the clouds of the bulge and is able to provide for us a fantastic image of our galactic core:

The bright areas are intense energy sources believed to be driven by a black hole. This artists impression below demonstrates what a black hole might look like:

A closer look in the X-ray reveals an area in the direction of the constellation Sagittarius. This source of energy is called Sagittarius A, and the source object is called Sagittarius A* (a-star). Sagittarius A* is believed to be the Supermassive Black Hole. But why is it called a Supermassive Black Hole? A "normal" black hole is the result of a massive star's sudden exhaustion when it burns up its fuel.

Because the star is so massive, it collapses on itself creating a black hole. This will be discussed in the Star section. Because the center of a galaxy can contain thousands of stars, and because we are able to calculate the gravity effect of the black hole at the center, we learn the mass of this black hole is much much greater than a stellar black hole.

Of course, we have yet to see a black hole so we are not 100% certain that black holes exists - but we do have compelling evidence. The image below is an animated .gif that shows the region surrounding Sagittarius A*. The stars close to the center are moving rapidly compared to the background stars (you may have to reload or re-visit the page to reset the animation).

The motions of the stars are a result of the massive gravity generated by this region. This evidence, the energy generated by Sagittarius A* and the images in the X-ray are all very compelling evidence to support that a black hole is at the heart of our galaxy - as a matter of fact, many of Astronomers believe that supermassive black holes are at the heart of almost every galaxy.

Is there any reason for concern? No. The galaxy will not be swallowed whole by this black hole. But this information is valuable. We can apply our knowledge to other galaxies and perhaps unlock the door to reveal how a galaxy is formed and evolves.


Active Galaxies

Active galaxies are galaxies that have a small core of emission embedded at the center of an otherwise typical galaxy. This core is typically highly variable and very bright compared to the rest of the galaxy.

For normal galaxies, we think of the total energy they emit as the sum of the emission from each of the stars found in the galaxy, but in active galaxies, this is not true. There is a great deal more emitted energy in active galaxies than there should be and this excess energy is found in the infrared, radio, UV, and X-ray regions of the electromagnetic spectrum. The energy emitted by an active galaxy, AGN for short, is anything but normal. So what is happening in these galaxies to produce such an energetic output?

Most, if not all, normal galaxies have a supermassive black hole at their center. In an active galaxy, its supermassive black hole is accreting material from the galaxy's dense central region. As the material falls in toward the black hole, angular momentum will cause it to spiral in and form into a disk. This disk, called an accretion disk, heats up due to the gravitational and frictional forces at work.

This illustration shows the different features of an active galactic nucleus (AGN). The extreme luminosity of an AGN is powered by accretion onto a supermassive black hole. Some AGN have jets, while others do not. (Credit: Aurore Simonnet, Sonoma State University)

Models of active galaxies also include a region of cold gas and dust, thought to be in the shape of a giant donut with the black hole and accretion disk nestled in the donut's hole. In about one out of ten AGN, the black hole and accretion disk produce narrow beams of energetic particles and ejects them outward in opposite directions away from the disk. These jets, which emerge at nearly the speed of light, become a powerful source of radio wave emission.

The properties of an active galaxy are determined by the black hole's mass, the rate of accretion onto the black hole, whether or not it has a powerful jet, and the angle at which we view the galaxy. Radio galaxies, quasars, and blazars are AGN with strong jets that can travel outward into large regions of intergalactic space. Some of the apparent differences between types of AGN are due to our having different orientations with respect to the disk. With blazars and quasars, we are looking down the jet.

Active galaxies are intensely studied at all wavelengths. Since they can change their behavior on short timescales, it is useful to study them simultaneously at all energies. X-ray and gamma-ray observations have proven to be important parts of this multiwavelength approach since many high-energy quasars emit a large fraction of their power at such energies. The X-rays in AGN originate from very near the black hole, so X-ray studies can provide scientists with unique insights into the physical processes occurring in the central engine. In addition, gamma-ray observations alone can provide valuable information on the nature of particle acceleration in the quasar jet and clues as to how the particles interact with their surroundings.

The left image shows a ground-based composite optical and radio view of elliptical galaxy NGC 4261. Photographed in visible light (white) the galaxy appears as a fuzzy disk of hundreds of billions of stars. A radio image (orange) shows a pair of opposed jets emanating from the nucleus and spanning a distance of 88,000 light-years. The image on the right shows a Hubble Space Telescope view of the core of NGC 4261. A giant disk of cold gas and dust measures about 300 light years across and could be fueling a possible black hole at the core of the galaxy. The disk is tipped enough (about 60 degrees) to provide astronomers with a clear view of its bright hub, which presumably harbors the black hole. (Credit: NRAO, Cal Tech, Walter Jaffe/Leiden Observatory, Holland Ford/JHU/STScI, and NASA)


Gravitational Lensing

As we saw in Black Holes and Curved Spacetime, spacetime is more strongly curved in regions where the gravitational field is strong. Light passing very near a concentration of matter appears to follow a curved path. In the case of starlight passing close to the Sun, we measure the position of the distant star to be slightly different from its true position.

Now let’s consider the case of light from a distant galaxy or quasar that passes near a concentration of matter such as a cluster of galaxies on its journey to our telescopes. According to general relativity, the light path may be bent in a variety of ways as a result we can observe distorted and even multiple images (Figure 5).

Figure 5: Gravitational Lensing. This drawing shows how a gravitational lens can make two images. Two light rays from a distant quasar are shown being bent while passing a foreground galaxy they then arrive together at Earth. Although the two beams of light contain the same information, they now appear to come from two different points on the sky. This sketch is oversimplified and not to scale, but it gives a rough idea of the lensing phenomenon.

Gravitational lenses can produce not only double images, as shown in Figure 5, but also multiple images, arcs, or rings. The first gravitational lens discovered, in 1979, showed two images of the same distant object. Eventually, astronomers used the Hubble Space Telescope to capture remarkable images of the effects of gravitational lenses. One example is shown in Figure 6.

Figure 6: Multiple Images of a Gravitationally Lensed Supernova. Light from a supernova at a distance of 9 billion light-years passed near a galaxy in a cluster at a distance of about 5 billion light-years. In the enlarged inset view of the galaxy, the arrows point to the multiple images of the exploding star. The images are arranged around the galaxy in a cross-shaped pattern called an Einstein Cross. The blue streaks wrapping around the galaxy are the stretched images of the supernova’s host spiral galaxy, which has been distorted by the warping of space. (credit: modification of work by NASA, ESA, and S. Rodney (JHU) and the FrontierSN team T. Treu (UCLA), P. Kelly (UC Berkeley), and the GLASS team J. Lotz (STScI) and the Frontier Fields team M. Postman (STScI) and the CLASH team and Z. Levay (STScI))

General relativity predicts that the light from a distant object may also be amplified by the lensing effect, thereby making otherwise invisible objects bright enough to detect. This is particularly useful for probing the earliest stages of galaxy formation, when the universe was young. Figure 7 shows an example of a very distant faint galaxy that we can study in detail only because its light path passes through a large concentration of massive galaxies and we now see a brighter image of it.

Figure 7: Distorted Images of a Distant Galaxy Produced by Gravitational Lensing in a Galaxy Cluster. The rounded outlines show the location of distinct, distorted images of the background galaxy resulting from lensing by the mass in the cluster. The image in the box at lower left is a reconstruction of what the lensed galaxy would look like in the absence of the cluster, based on a model of the cluster’s mass distribution, which can be derived from studying the distorted galaxy images. The reconstruction shows far more detail about the galaxy than could have been seen in the absence of lensing. As the image shows, this galaxy contains regions of star formation glowing like bright Christmas tree bulbs. These are much brighter than any star-formation regions in our Milky Way Galaxy. (credit: modification of work by NASA, ESA, and Z. Levay (STScI))

We should note that the visible mass in a galaxy is not the only possible gravitational lens. Dark matter can also reveal itself by producing this effect. Astronomers are using lensed images from all over the sky to learn more about where dark matter is located and how much of it exists.


Mystery Object in Cygnus A Galaxy

By: Camille M. Carlisle January 13, 2017 2

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Astronomers have discovered an object in the active galaxy Cygnus A that wasn’t there before.

The galaxy Cygnus A "shines" in radio frequencies (seen here), coming from relativistic electrons zipping along jets shot out from the central black hole and deposited in giant "radio lobes." (The lobes extend outward roughly 10 times farther than the galaxy itself, which is invisible in this image.)
NRAO / AUI

Last week at the American Astronomical Society meeting in Grapevine, Texas, astronomers made an announcement that’s caught the interest of several researchers: a very bright something has appeared in a well-known galaxy.

That galaxy is the elliptical Cygnus A. Cygnus A is one of the brightest radio sources in the sky. It lies approximately 800 million light-years from us (redshift of 0.056). In its core sits a supermassive black hole madly eating and cocooned in gas, while two jets shoot out to either side and light up the intergalactic medium. This activity produces the radio radiation that makes Cygnus A so bright.

Using the recently upgraded Karl G. Jansky Very Large Array (VLA) in New Mexico, Rick Perley (NRAO) and colleagues took a gander at Cygnus A — the first time the instrument has looked at the galaxy since 1989. (Apparently astronomers spent so much VLA time observing the galaxy in the 1980s that they didn’t feel the need to look again, Perley joked January 6th in his AAS presentation.) The new observations showed a surprise: a new, secondary object just southwest of the central black hole. This object wasn’t in the 1989 radio image. Additional, higher-resolution observations with the Very Long Baseline Array also picked up the object, clearly distinct from the galaxy’s nucleus. It’s roughly 1,300 light-years from the center.

The whatever-it-is is about twice as bright as the brightest known supernova at these frequencies. In fact, it’s much brighter than just about any transitory radio signal known, except for accreting supermassive black holes and tidal disruption events, outbursts created when a black hole eats a star.

The team scoured other archives and found the object in 2003 Keck infrared observations and, more iffily, in some images from Hubble. (The object is so red that it doesn’t show up well at optical wavelengths, and in this range the space telescope’s resolution isn’t as good as that of Keck’s adaptive optics.)

This false-color infrared image from the Keck II telescope shows the galaxy Cygnus A. Its central supermassive black hole is the large red-black splotch, but this 2003 image reveals a second, mystery source (circled) nearby.
G. Canalizo et al. / Astrophysical Journal 2003

The science session’s attendees were aflutter with curiosity. Claire Max, who serves as director of the University of California Observatories (which manages both the Keck and Lick Observatories), went back and dug through Keck data and discovered that, in fact, astronomers had already discovered this source. In 2003 she, Gabriela Canalizo (now at University of California, Riverside), and colleagues had stumbled upon the mystery source. They, too, had gone back and found it in some Hubble images and not others — they weren’t sure whether that was because the source was flickering, or just that Hubble hadn’t looked long enough to consistently see it.

The team determined that the whatchamacallit wasn’t a foreground object in the Milky Way, nor a cluster of young stars in Cygnus A. Rather, it seemed to be a compact cluster of old, red stars, with all the trappings of being the stripped-down core of a much smaller galaxy that Cygnus A had eaten. That minor merger might also explain why the big galaxy’s black hole has “turned on,” the astronomers suggested in their 2003 Astrophysical Journal paper.

On the other hand, Canalizo and colleagues went on to suggest in 2004 that the source might instead be a peek at the hot inner rim of the dusty doughnut enshrouding the black hole.

Perley’s team favors a merger, too. But he advocated instead that the radiation might come from a second black hole, the leftover core of the eaten galaxy. If so, then Cygnus A is one of a few galaxies that seems to host a central binary black hole.

At the end of his presentation Perley called for others to look through their archival observations so that astronomers can pinpoint when this source appeared. His team is also looking in X-ray, but given that the central nucleus is so bright, they’re not optimistic of their chances of seeing something, unless there’s some variability. A formal paper and press release (with cool images!) are in the works, and when they’re out we’ll update you with more info.

Richard A. Perley et al. “Serendipitous Discovery of a Radio Transient in the Luminous Radio Galaxy Cygnus A.” 229th American Astronomical Society. Abstract 319.06.

Gabriela Canalizo et al. “Penetrating Dust Tori in AGN.” Penetrating Bars through Masks of Cosmic Dust. 2004.


NGC 3190 bunch — Leo I group

If NGC 3226-27 is your first stop you don't have to go far to find our next batch of furry galactic catkins. The NGC 3190 group appears just 2° north of Gamma (γ) Leonis on a line to Zeta (ζ) Leonis in a field peppered with bright telescopic stars ranging from magnitude 7.5 to 10.5. This tight clump of four galaxies spans just 17′wide, which means you can use magnifications of 200× or more and keep them all in the same field of view.

Comprising three spiral galaxies and one elliptical, the NGC 3190 group (Hickson 44) is rich in variety for the visual observer. The bizarre NGC 3187 appears at top with NGC 3193, NGC 3190, and NGC 3185 in a row from left to right. North is at upper right.
Stephen Leshin

The galaxy NGC 3193 (magnitude 10.9, 2.0′ × 2.0′) is a classic elliptical — round and fuzzy with a brighter core and near-stellar nucleus. A 9.6-magnitude star pins its northern border. While the spiral NGC 3190 (magnitude 11.1, 4.4′ × 1.5′) appears a tad fainter it was my favorite with an obviously elongated disk and a bright, extended nuclear region that swaddled a bloated, starlike nucleus. NGC 3185 (magnitude 12, 2.3′ × 1.6′) was a small, faint oval oriented northwest-southeast with a stellar core and slightly brighter inner disk.

I'd hoped to see the barred spiral NGC 3187's (magnitude 13.4, 3.6′ × 1.6′) wacky spiral arms, flung out on either side like a swing dancer, but this is a faint, diffuse object, and the best I could do was make out a misty, elongated disk tipped northwest-southeast at 257× with averted vision. Both NGC 3127 and neighboring NGC 3190 exhibited warped disks, evidence of tidal interactions common among galaxies in compact clusters.


Hubble Snaps Breathtaking New Image of NGC 2336

This Hubble image shows NGC 2336, a barred spiral galaxy located 109 million light-years away in the constellation of Camelopardalis. The color image was made from separate exposures taken in the visible and near-infrared regions of the spectrum with Hubble’s Advanced Camera for Surveys (ACS). Three filters were used to sample various wavelengths. The color results from assigning different hues to each monochromatic image associated with an individual filter. Image credit: NASA / ESA / Hubble / V. Antoniou / Judy Schmidt.

NGC 2336 is a barred spiral galaxy located in the northern constellation of Camelopardalis.

Otherwise known as LEDA 21033 and UGC 3809, it lies at a distance of 109 million light-years.

NGC 2336 is a member of a small galaxy group known as the NGC 2336 group.

It also forms a non-interacting pair with the spiral galaxy IC 467.

“NGC 2336 was discovered in 1876 by the German astronomer Wilhelm Tempel, using a 28-cm telescope,” Hubble astronomers said.

“This Hubble image is so much better than the view Tempel would have had — Hubble’s main mirror is 2.4 m across, nearly ten times the size of the telescope Tempel used.”

NGC 2336 has a small bar and at least eight spiral arms.

“NGC 2336 stretches an immense 200,000 light-years across,” the researchers said.

“Its spiral arms are glittered with young stars, visible in their bright blue light.”

“In contrast, the redder central part of the galaxy is dominated by older stars.”

“In 1987, NGC 2336 experienced a Type-Ia supernova, the only observed supernova in the galaxy since its discovery 111 years earlier.”


Types of Galaxies

Galaxies can be classified in several ways. The most common is a system developed by Edwin Hubble, which is based on the shapes of galaxies.

The most beautiful galaxies are called spirals. The Milky Way is a spiral, and so is the Andromeda galaxy (M31).

Spirals are flat disks of stars with bright bulges in their centers. Spiral arms wrap around these bulges. Spiral arms probably form as the result of waves that sweep through the galactic disk. Like the waves on the ocean, these "density waves" don't carry material with them. Instead, they influence matter as they pass by. In the case of galaxies, they squeeze clouds of interstellar gas, triggering new star formation. Some newborn stars are massive, hot, and bright, so they make the spiral arms appear bright. These massive stars are blue or white, so the spiral arms look blue-white, too. The gaps between the arms contain older stars, which are not as bright.

In some spirals, a wave organizes the stars in the center into a bar. The arms of barred galaxies spiral outward from the ends of the bar. The Milky Way falls into this class of spirals.

A second class of galaxy is the ellipticals. Like spirals, they are named for their shapes: they look like fat, fuzzy footballs. Instead of spreading out into a thin disk, as they do in spirals, the stars in ellipticals wrap completely around the galaxy's heart in all directions.

The largest galaxies in the universe are giant ellipticals. They can contain a trillion stars or more, and span as much as one million light-years -- about 10 times the diameter of the Milky Way. Like many large spirals, most of them appear to contain "supermassive" black holes at their hearts -- star-gobbling monsters that are as much as three billion times as massive as the Sun.

The final class of galaxies contains a hodge-podge of shapes -- anything that looks neither spiral nor elliptical. These are the irregulars. These galaxies have no identifiable form. Their stars, gas, and dust spread randomly. These are the smallest galaxies, and may contain as few as one million stars. They may be like the "building blocks" that came together to form the first large galaxies. Many small irregular galaxies orbit the Milky Way.

Astronomers also categorize galaxies by how much energy they produce in their cores. A particular class is called "active" galaxies, because they produce much more energy than "normal" galaxies.

The most powerful active galaxies are quasars. They are among the brightest and most distant objects in the universe. A quasar may emit more energy than an entire galaxy of stars from a region no bigger than our own solar system. Astronomers believe these objects contain supermassive black holes at their hearts, which are encircled by disks of gas. A black hole is an object that is squeezed together so tightly that it has extremely strong gravity. Its gravity is so powerful that nothing can escape from it -- not even light. As gas spirals toward the black hole, it is heated to billions of degrees, so it emits enormous amounts of energy, and the quasar shines brightly.


Watch the video: Κβάζαρ: Τα πιο φωτεινά αντικείμενα του σύμπαντος. Astronio #24 (December 2022).