Tammy was a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.
(Tammy passed away in early 2015... she will be missed)
As we know, Jupiter’s Southern Equatorial Belt has been missing beneath its icy clouds for almost a year now. While astronomers are able to use instruments like Keck – complete with infrared and adaptive optics – we here on Earth have to take our views of Jupiter a little more naturally.
As you can see from this webcam image given to us by John Chumack, even our thin earthly clouds can’t quite hide bright Jupiter. It has returned to the same ruddy, lined face that most of us fell in love with the first time we observed it. Stunning details? No… Because this is how Jupiter really looks when you first glimpse it in the eyepiece.
Right now the westering Jupiter isn’t in the best of positions for extended observing, but it is at a comfortable height and a comfortable time. While it might be tempting to throw a huge amount of magnification its way, it actually makes the view worse rather than improving it. With steady seeing condtions, around 150-200X is ideal – reducing the magnification even lower if the atmosphere is turbulent. You’ll find you’ll also have greater success using your orthoscopic or plossl design eyepieces, too. Got color filters? Go ahead and experiment! Blues, reds and yellows all cause contrast change which can reveal subtle details. As unusual as it may sound, sketching also helps. You don’t need to be a Rembrandt. Just the act of translating what the eye sees onto paper greatly improves your “human” focus.
Don’t forget the galiean moons! As you can see, Europa can look like a world of its own. While larger aperture instruments are able to resolve events like shadow transits, don’t feel left out if you have a small telescope. It’s very exciting to witness one of Jupiter’s satellites being eclipsed by the parent planet – or disappearing as it passes in front. There are even times when the moons eclipse each other! Go on… Take advantage of the early evening hours and enjoy Jupiter.
Because you never know when the perfect moment seeing will arrive…
Many thanks to John Chumack of Galactic Images for sharing his recent image of Jupiter with us.
If you like keeping track of somewhat obscure meteor showers, tonight will be one of your best opportunities to spot the Delta Leonids. What’s the history of these meteors and when and where do you look? Let’s go outside and find out…
The Delta Leonids aren’t ancient and first came to attention during the early 20th century when W. F. Denning first made record of them in 1911. They were described as slow, with trains – but 16 independent observers report one of them as being at least six times as bright as the planet Venus. At the time, the fall rate was an average of 7 per hour.
Studies continued in 1924 and 1930 as scientists endeavored to pinpoint a radiant and an orbital stream. The results were rather inconclusive and the validity of the stream left to speculation. Are they Delta Leonids? Or the precursors of the Beta stream? From 1961 to 1965 a radio echo survey was employed and the results showed Earth passing through the stream between February 9th to March 12th. After several years of observation, the Western Australia Meteor Section has provided the most positive conculsions to date. While the stream cannot be attributed to any particular comet orbit, it does exist and peaks on (or about) February 26th.
If you’re out and about tonight, keep watch around the constellation of Leo… it will be relatively high in the sky around 10-11:00 pm local time. You’ll find its signature “backwards question mark” asterism along the ecliptic plane – the imaginary path the Sun and Moon take across the sky. With a typical magnitude of 2.8, these slow moving travellers will stand out against a fainter backdrop of stars. However, don’t expect to see a huge amount of activity, because the fall rate only averages about 5 per hour.
So why bother? It won’t hurt to keep an eye on the sky if you’re out walking your dog, or perhaps enjoying social activities which take you out to your car. The Delta Leonids are a temporary meteor stream and won’t be around forever. Catch ’em while you can!
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If you’re an early riser, then perhaps you’ve noticed Kepler’s Laws in action? No, it’s not a new Bruce Willis movie, just the inevitable pairing of the waning crescent Moon and shining Venus. As you can see from this great photo taken last month by John Chumack, it happens as regular as clockwork… and it’s about to happen again. But what is it about such pairings that command our attention? Step inside and find out!
According to the Sky & Telescope press release, the brightest planet and the eerie waning crescent Moon will create an arresting sky scene low in the southeast in the early dawn of Monday, February 28th, and Tuesday, March 1st. “These are the two brightest astronomical objects in the sky after the Sun,” says Alan MacRobert, a senior editor of Sky & Telescope magazine. “They’ll certainly catch your eye, if you look low in the southeast about 60 to 40 minutes before sunrise — weather permitting.”
Venus will be shining to the Moon’s lower left on the morning of Monday Feb. 28th. The next morning Venus will be to the Moon’s right or upper right. Although they look close together, they’re not. Venus is currently 400 times farther away than the Moon. It’s at a distance of 8.8 light-minutes (the distance light takes to travel that far), compared to the Moon’s distance of 1.3 light-seconds. In miles, that’s 99 million miles for Venus and just 249,000 miles for the Moon. (In fact, you may have driven cars enough miles to get to the Moon.) And despite appearances, Venus is 3½ times wider than the Moon’s diameter.
Locator Chart Courtesy of Sky & Telescope Magazine
“Why do people care about this?” asks MacRobert. “Because some people know we need to look up beyond our own little world — and recognize where we are as part of nature, part of the universe. So many of us live our busy little ant-hill lives without ever noticing the gigantic universe beyond the anthill. A lot of people don’t even know you can see alien planets from your driveway while you’re unlocking the car to go to work.”
But just what is it about such a celestial scene that draws our eye like no other? When it comes to our eyes, almost every photoreceptor has one ganglion cell receiving data in the fovea. That means there’s almost no data loss and the absence of blood vessels in the area means almost no loss of light either. There is direct passage to our receptors – an amazing 50% of the visual cortex in the brain! Since the fovea doesn’t have rods, it isn’t sensitive to dim lights. That’s another reason why the conjunctions are more attractive than the surrounding starfields. Astronomers know a lot about the fovea for a good reason: it’s is why we learn to use averted vision. We avoid the fovea when observing very dim objects in the eyepiece.
“Your eye is like a digital camera,” explains Dr. Stuart Hiroyasu, O.D., of Bishop, California. “There’s a lens in front to focus the light, and a photo-array behind the lens to capture the image. The photo-array in your eye is called the retina. It’s made of rods and cones, the fleshy organic equivalent of electronic pixels.” Near the center of the retina lies the fovea, a patch of tissue 1.5 millimeters wide where cones are extra-densely packed. “Whatever you see with the fovea, you see in high-definition,” he says. The fovea is critical to reading, driving and even watching television. The fovea has the brain’s attention. The field of view of the fovea is only about five degrees wide.” When Venus and the crescent Moon are close to that narrow angle, it signals to the brain, “this is worth watching!”
Let’s pretend we’re a photoreceptor. If a light were to strike us, we’d be “on” – recording away. If we were a ganglion cell, the light really wouldn’t do much of anything. However, the biological recorder would have responded to a pinpoint of light, a ring of light, or a light with a dark edge to it. Why? Light in general just simply doesn’t excite the ganglion, but it does wake up the neighbor cells (as does hooting and screaming while pointing at the morning sky). A small spot of light makes the ganglion go crazy, but the neighbors don’t pay much attention (unless you’re in your pajamas cleaning the snow off your car). However, a ring of light makes the neighbors go nuts (and their dogs) and the ganglion turns off. It’s all a very complicated response to a simple scene, but still fun to understand why we are compelled to look!
According to SpaceWeather: “Fast-growing active region 1161 erupted this morning, producing an M6.6-class solar flare at 1011 UT. The almost-X category blast was one of the strongest flares in years and continued the week-long trend of high solar activity.” Just how awesome is that? Then take a look at these white light solar images done by John Chumack…
While today’s activity isn’t supposed to impact Earth in a negative manner, who knows what it might produce in the days ahead? Just ask NOAA!
“A G1 (minor) geomagnetic storm continues. What might have been three hits of shocks/CMEs seems to have merged to be just one interplanetary shock/CME structure. Look for about another day’s worth of geomagnetic activity, pending additional treats in the solar wind. Elsewhere Region 1158 had another R2 (moderate) radio blackout, and fast-growing new Region 1162 likely generated an R1 (minor) event.”
Sunspot 1158 on 02-17-11 by John Chumack
With 1158 nearing the limb and wonderfully active, now is the time for solar observers to try and catch the “Wilson Effect” – an effect in which the penumbra of a sunspot appears narrower in the direction toward the Sun’s center.
While you’re at it, it doesn’t hurt to keep watch for auroral activity tonight and in the days ahead – despite the lunar interference. With satellite communications impacted in my area, I’m anxious to see what the nights – and days – bring!
Z Canis Major - Credit: Palomar Observatory, courtesy of Caltech
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Heads up, weekend warriors! With very little Moon to contend with, it would be a great time to observe the bright outburst of the pre-main sequence variable star, Z Canis Major. It has gained more than two magnitudes and is well within binocular and small telescope range.
From the AAVSO Special Notice compiled by Elizabeth O. Waagen: “John Bortle, Stormville, NY, reports that the pre-main sequence binary variable Z CMa is in outburst, according to his observation of 2011 February 4.0 UT at visual magnitude 8.5. Observations in the AAVSO International Database confirm this outburst, which may have begun as long ago as April 2010, when it began brightening slightly from visual magnitude 10.7. When Z CMa emerged from its seasonal gap in November 2010, it was already 9th magnitude.
Locator Chart Courtesy of AAVSO
The current outburst is as bright as the one that occurred in 2008, the brightest in the star’s known history. Z CMa is a very interesting object, a binary composed of a Herbig Be star and an FU Ori star. The Herbig star is embedded in nebulosity. The system is an x-ray source and has an x-ray jet. According to Stelzer et al. (2009, Astronomy & Astrophysics v.499, p.529, and astro-ph arXiv:0903.4060), the FU Ori star is the source of both the optical outbursts and the x-ray emission. Observations of Z CMa (RA 07:03:43.16 Dec -11:33:06.2) are strongly encouraged, both during the current outburst and throughout the observing season. With its range of visual magnitude ~8.0 – 10.5, it is an excellent visual observing target.”
Is there any place in the night sky which stimulates our imaginations more than the famous Horsehead? This area of dark dust painted over the smokey veil of emission nebula is one of the most often photographed and visually sought-after regions in Orion. How many of us have used (or bought) a special filter just to see it with your own eyes? Then behold it once again in all of its glory – and all of its mysteries…
“I am happy to present my first image of 2011 with an object that has been long on my target list.” says astrophotographer, Ken Crawford. “This is the famous Horsehead Nebula which is formed by a dark cloud of dust and gas that forms a silhouette against the glow of IC434 behind it. There has been a lot of research done in this region because of the star forming fronts and surrounding molecular clouds with condensing areas that show up as small red clumps. These clumps are glowing red because of the rising temperatures inside are getting hot enough to be seen through the gas surrounding it as they become new stars. These condensing, glowing clumps are called Herbig-Haro objects and can be seen below the Horsehead on the left side and in the cropped image. There is a young new star in the top of the “head” area that sits in a small nebula and has the name B33-1.”
But radiation from this hot star is eroding the stellar nursery. When E.E. Barnard discovered it in 1913, he noted that the edges were “sharp” and “well defined”. Not any more. In just about a century the UV radiation of this O9 star is beginning to show its slow destruction of the cloud…. and that’s not all that is eating away at the familiar equine shape. “We find evidence for a lozenge-shaped clump in the ‘throat’ of the horse, which is not seen in emission at shorter wavelengths. We label this source B33-SMM2 and find that it is brighter at submillimetre wavelengths than B33-SMM1.” says D. Ward-Thompson, et al. “We calculate the stability of this core against collapse and find that it is in approximate gravitational virial equilibrium. This is consistent with it being a pre-existing core in B33, possibly pre-stellar in nature, but that it may also eventually undergo collapse under the effects of the HII region.”
However, destruction is not all this beautiful image reveals. “The bright nebula in the lower left is called NGC2023 and is called a reflection nebula because the blue wavelengths of light are reflected by the dust and gas around the hot blue star.” says Crawford. “There are also Herbig-Haro objects in this active region of star formation. This reflection nebula provides a beautiful contrast of textures and colors that help make the Horsehead nebula one of my all time favorites.”
The bright galaxy NGC 3621, captured here using the Wide Field Imager on the 2.2-metre telescope at ESO’s La Silla Observatory in Chile, appears to be a fine example of a classical spiral. But it is in fact rather unusual: it does not have a central bulge and is therefore described as a pure-disc galaxy.
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What could be more eye-catching than a picture perfect pure disk galaxy? In itself it is untouched – not yet combined with a neighboring elliptical or rouge spiral. This is the way we dream of seeing a distant companion… a virgin galaxy awaiting further growth. In a Universe dominated by clusters of galaxies and violent collisions, just how often does a thin, flat plate of stars occur?
According to the ESO Press Release, NGC 3621 is a spiral galaxy about 22 million light-years away in the constellation of Hydra (The Sea Snake). It is comparatively bright and can be seen well in moderate-sized telescopes. This picture was taken using the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. The data were selected from the ESO archive by Joe DePasquale as part of the Hidden Treasures competition. Joe’s picture of NGC 3621 was ranked fourth in the competition.
This galaxy has a flat pancake shape, indicating that it hasn’t yet come face to face with another galaxy as such a galactic collision would have disturbed the thin disc of stars, creating a small bulge in its center. Most astronomers think that galaxies grow by merging with other galaxies, in a process called hierarchical galaxy formation. Over time, this should create large bulges in the centers of spirals. Recent research, however, has suggested that bulgeless, or pure-disc, spiral galaxies like NGC 3621 are actually fairly common. But just how common?
This galaxy is of further interest to astronomers because its relative proximity allows them to study a wide range of astronomical objects within it, including stellar nurseries, dust clouds, and pulsating stars called Cepheid variables, which astronomers use as distance markers in the Universe. In the late 1990s, NGC 3621 was one of 18 galaxies selected for a Key Project of the Hubble Space Telescope: to observe Cepheid variables and measure the rate of expansion of the Universe to a higher accuracy than had been possible before. In the successful project, 69 Cepheid variables were observed in this galaxy alone.
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This sequence gives a close-up view of the spiral galaxy NGC 3621. This picture was taken using the Wide Field Imager (WFI) at ESO’s La Silla Observatory in Chile. NGC 3621 is about 22 million light-years away in the constellation of Hydra (The Sea Snake). It is comparatively bright and can be well seen in moderate-sized telescopes. The data from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile used to make this image were selected from the ESO archive by Joe DePasquale as part of the Hidden Treasures competition.
One of the fascinating things in viewing this image (for me, at least) is seeing all the star-forming regions on the periphery of the galaxy itself. It reminds me of the NGC objects we see in both M31 and M33 (another pure disk galaxy, too). While smaller backyard telescopes are never going to be able to resolve these kinds of details, I can’t help but wonder what larger, professional level equipment can do on a visual level. While I’m at it, my mind also wonders about what we’ve learned recently of the reliability of Cepheid variables as indicators of distance, too. Is this the end all of information? Nah. Because we’re living in a “pure disk” galaxy. Yeah. You heard me right… The Milky Way fits the model, too!
According to a study done by Juntai Shen (Shanghai Astronomical Observatory), et al: “Bulges are commonly believed to form in the dynamical violence of galaxy collisions and mergers. Here we model the stellar kinematics of the Bulge Radial Velocity Assay (BRAVA), and find no sign that the Milky Way contains a classical bulge formed by scrambling pre-existing disks of stars in major mergers. Rather, the bulge appears to be a bar, seen somewhat end-on, as hinted from its asymmetric boxy shape. We construct a simple but realistic N-body model of the Galaxy that self-consistently develops a bar. The bar immediately buckles and thickens in the vertical direction. As seen from the Sun, the result resembles the boxy bulge of our Galaxy. The model fits the BRAVA stellar kinematic data covering the whole bulge strikingly well with no need for a merger-made classical bulge. The bar in our best fit model has a half-length of ~ 4kpc and extends 20 degrees from the Sun-Galactic Center line. We use the new kinematic constraints to show that any classical bulge contribution cannot be larger than ~ 8% of the disk mass. Thus the Galactic bulge is a part of the disk and not a separate component made in a prior merger. Giant, pure-disk galaxies like our own present a major challenge to the standard picture in which galaxy formation is dominated by hierarchical clustering and galaxy mergers.”
Move over, NGC 3621… We’re both commoners.
Many thanks to the European Southern Observatory (ESO) for providing the press release and awesome images!
Just before the holidays, UT reported about about the Growing Storm On Saturn and showed us the Cassini images. Now more than a month has passed and the white scar of the raging atmosphere has escalated to an incredible size… Nearly 10 Earths wide!
Despite sub-zero temperatures and significant snow cover, at least one dedicated observer has been getting up early to observe what we rarely see – a change in Saturn’s pale golden face. “I was out from 4:30am to 6:00am early Saturday morning. I brushed all the snow off my Dome, and spent an hour or so shooting Saturn with its Big White Storm brewing in the cloud tops.” say John Chumack of Dayton, Ohio. “The seeing conditions were not the best, but I went for it anyway, after the high cirrus clouds moved out of the way, I had to try! -3F Temps in my backyard in Dayton, OH nearly killed my attempt.”
And temperatures like that are warm compared to Saturn’s surface. Depending on the depth of the atmosphere, it could be anywhere from -218.47F to -308.47. Unlike an Alberta Clipper here on Earth, Saturn is constantly having hurricane-like storms. However, few are easily visible in the average telescope. “The storm is enormous.” said John. “It’s no wonder we can see it from Earth, since Saturn at the time of this shot was about 865.2 million miles away or 1.392 billion km from us!”
But there’s more than just a storm hiding in John’s image. Thanks to a little ‘negative thinking’ he was also able to capture five tiny moons circling around Saturn’s icy ring system – Rhea, Dione, Enceladus, Mimas, and Tethys.
“My feet and fingers were numb by the time I was done, even with gloves on, nothing like having to touch frozen metal to point the telescope and run the focusers. Even the hand control paddles were having a tough time with the extreme temps, the LCD went blank and stopped working.” said John. “Heck, I nearly got freezer burned myself!!!”
Yeah, but what a view!
Many thanks to John Chumack of Galactic Images for braving the weather and sharing his work!
[/caption]No Princess is sending holographic help messages. No Hans Solo is warming up a Millenium Falcon to jump into hyperdrive. We don’t even have a Death Star waiting around the corner. But, what we do have is evidence that astronomers have pushed the Hubble Space Telescope to its limits and have seen further back in time than ever before. “We are looking back through 96% of the life of the universe, and in so doing, we have found just one galaxy, but it is one, but it is a remarkable object. The universe was only 500 million years old at that time versus it now being thirteen thousand-seven hundred million years old. ” said Garth Illingworth, Ames Research Scientist. We know about the Hubble Ultra Deep Field, but we invite you to boldy go on…
While studying ultra-deep imaging data from the Hubble Space Telescope, an international group of astronomers have found what may be the most distant galaxy ever seen, about 13.2 billion light-years away. “Two years ago, a powerful new camera was put on Hubble, a camera which works in the infrared which we had never really good capability before, and we have now taken the deepest image of the universe ever using this camera in the infrared.” said Garth Illingworth, professor of astronomy and astrophysics at the University of California, Santa Cruz. “We’re getting back very close to the first galaxies, which we think formed around 200 to 300 million years after the Big Bang.” The study pushed the limits of Hubble’s capabilities, extending its reach back to about 480 million years after the Big Bang, when the universe was just 4 percent of its current age. The dim object, called UDFj-39546284, is a compact galaxy of blue stars that existed 480 million years after the Big Bang, only four percent of the universe’s current age. It is tiny. Over one hundred such mini-galaxies would be needed to make up our Milky Way.
The farthest and one of the very earliest galaxies ever seen in the universe appears as a faint red blob in this ultra-deep–field exposure taken with NASA's Hubble Space Telescope. This is the deepest infrared image taken of the universe. Based on the object's color, astronomers believe it is 13.2 billion light-years away. (Credit: NASA, ESA, G. Illingworth (University of California, Santa Cruz), R. Bouwens (University of California, Santa Cruz, and Leiden University), and the HUDF09 Team)
Illingworth and UCSC astronomer Rychard Bouwens (now at Leiden University in the Netherlands) led the study, which will be published in the January 27 issue of Nature. Using infrared data gathered by Hubble’s Wide Field Planetary Camera 3 (WFC3), they were able to see dramatic changes in galaxies over a period from about 480 to 650 million years after the Big Bang. The rate of star birth in the universe increased by ten times during this 170-million-year period, Illingworth said. “This is an astonishing increase in such a short period, just 1 percent of the current age of the universe,” he said. There were also striking changes in the numbers of galaxies detected. “Our previous searches had found 47 galaxies at somewhat later times when the universe was about 650 million years old. However, we could only find one galaxy candidate just 170 million years earlier,” Illingworth said. “The universe was changing very quickly in a short amount of time.”
The Hubble Ultra Deep Field WFC3/IR Image. This Region of the Sky Contains the Deepest Optical and Near-Infrared Images Ever Taken of the Universe and is useful for finding star-forming galaxies at redshifts 8 and 10 (650 and 500 million years after the Big Bang, respectively). At UCSC and Leiden, we are using these data to better understand the properties of the first galaxies. Credit: Bouwen
According to Bouwens, these findings are consistent with the hierarchical picture of galaxy formation, in which galaxies grew and merged under the gravitational influence of dark matter. “We see a very rapid build-up of galaxies around this time,” he said. “For the first time now, we can make realistic statements about how the galaxy population changed during this period and provide meaningful constraints for models of galaxy formation.” Astronomers gauge the distance of an object from its redshift, a measure of how much the expansion of space has stretched the light from an object to longer (“redder”) wavelengths. The newly detected galaxy has a likely redshift value (“z”) of 10.3, which corresponds to an object that emitted the light we now see 13.2 billion years ago, just 480 million years after the birth of the universe. “This result is on the edge of our capabilities, but we spent months doing tests to confirm it, so we now feel pretty confident,” Illingworth said.
The galaxy, a faint smudge of starlight in the Hubble images, is tiny compared to the massive galaxies seen in the local universe. Our own Milky Way, for example, is more than 100 times larger. The researchers also described three other galaxies with redshifts greater than 8.3. The study involved a thorough search of data collected from deep imaging of the Hubble Ultra Deep Field (HUDF), a small patch of sky about one-tenth the size of the Moon. During two four-day stretches in summer 2009 and summer 2010, Hubble focused on one tiny spot in the HUDF for a total exposure of 87 hours with the WFC3 infrared camera.
“NASA continues to reach for new heights, and this latest Hubble discovery will deepen our understanding of the universe and benefit generations to come,” said NASA Administrator Charles Bolden, who was the pilot of the space shuttle mission that carried Hubble to orbit. “We could only dream when we launched Hubble more than 20 years ago that it would have the ability to make these types of groundbreaking discoveries and rewrite textbooks.”
To go beyond redshift 10, astronomers will have to wait for Hubble’s successor, the James Webb Space Telescope (JWST), which NASA plans to launch later this decade. JWST will also be able to perform the spectroscopic measurements needed to confirm the reported galaxy at redshift 10. “It’s going to take JWST to do more work at higher redshifts. This study at least tells us that there are objects around at redshift 10 and that the first galaxies must have formed earlier than that,” Illingworth said.
“After 20 years of opening our eyes to the universe around us, Hubble continues to awe and surprise astronomers,” said Jon Morse, NASA’s Astrophysics Division director at the agency’s headquarters in Washington. “It now offers a tantalizing look at the very edge of the known universe — a frontier NASA strives to explore.” How far back will we go? If you sit around a campfire watching the embers climb skywards and discuss cosmology after an observing night with your astro friends, someone will ultimately bring up the topic of space/time curvature. If you put an X on a balloon and expand it – and trace round its expanse – you will eventually return to your mark. If we see our beginnings, will we also eventually see our end coming up over the horizon? Wow… Pass the marshmallows, please. We’ve got a lot to think about.
Reader Info: Illingworth’s team maintains the First Galaxies website, with information about the latest research on distant galaxies. In addition to Bouwens and Illingworth, the coauthors of the Nature paper include Ivo Labbe of Carnegie Observatories; Pascal Oesch of UCSC and the Institute for Astronomy in Zurich; Michele Trenti of the University of Colorado; Marcella Carollo of the Institute for Astronomy; Pieter van Dokkum of Yale University; Marijn Franx of Leiden University; Massimo Stiavelli and Larry Bradley of the Space Telescope Science Institute; and Valentino Gonzalez and Daniel Magee of UC Santa Cruz. This research was supported by NASA and the Swiss National Science Foundation. Hubble Ultra Deep Field Image and Video courtesy of NASA/STSci.
NGC 6503, another example of a bulge-less galaxy with a massive halo and a small black hole.
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We only know they’re there because we can feel them in the dark… Feel their gravity, that is. Like a hide-and-go-seek game played on a moonless summer’s night, we only know that black holes and dark matter exist because we can feel the mass tagging us from beyond what our eyes can see. Are there monsters out there? Massive black holes have been found in galaxies with massive dark matter halos – but it doesn’t necessarily mean they’re in league with each other. Bring your bulge on over here to the dark side…
According to a press release from the Max-Planck-Institut; galaxies, such as our own Milky Way, consist of billions of stars, as well as great amounts of gas and dust. Most of this can be observed at different wavelengths, from radio and infrared for cooler objects up to optical and X-rays for parts that have been heated to high temperatures. However, there are also two important components that do not emit any light and can only be inferred from their gravitational pull. All galaxies are embedded in halos of so-called Dark Matter, which extends beyond the visible edge of the galaxy and dominates its total mass. This component cannot be observed directly, but can be measured through its effect on the motion of stars, gas and dust. The nature of this Dark Matter is still unknown, but scientists believe that it is made up of exotic particles unlike the normal (baryonic) matter, which we, the Earth, Sun and stars are made of.
The other invisible component in a galaxy is the supermassive black hole at its center. Our own Milky Way harbors a black hole, which is some four million times heavier than our Sun. Such gravity monsters, or even larger ones, have been found in all luminous galaxies with central bulges where a direct search is feasible; most and possibly all bulgy galaxies are believed to contain a central black hole. However, also this component cannot be observed directly, the mass of the black hole can only be inferred from the motion of stars around it. In 2002, it was speculated that there may exist a tight correlation between the mass of the Black Hole and the outer rotation velocities of galaxy disks, which is dominated by the Dark Matter halo, suggesting that the unknown physics of exotic Dark Matter somehow controls the growth of black holes. On the other hand, it had already been shown a few years earlier that black hole mass is well correlated with bulge mass or luminosity. Since larger galaxies in general also contain larger bulges, it remained unclear which of the correlations is the primary one driving the growth of black holes.
By studying galaxies embedded in massive dark halos with high rotation velocities but small or no bulges, John Kormendy and Ralf Bender tried to answer this question. They indeed found that galaxies without a bulge – even if they are embedded in massive dark matter halos – can at best contain very low mass black holes. Thus, they could show that black hole growth is mostly connected to bulge formation and not to dark matter. “It is hard to conceive how the low-density, widely distributed non-baryonic Dark Matter could influence the growth of a black hole in a very tiny volume deep inside a galaxy,” says Ralf Bender from the Max Planck Institute for Extraterrestrial Physics and the University Observatory Munich. John Kormendy, from the University of Texas, adds: “It seems much more plausible that black holes grow from the gas in their vicinity, primarily when the galaxies were forming.” In the accepted scenario of structure formation, galaxy mergers occur frequently, which scramble disks, allow gas to fall into the centre and thus trigger starbursts and feed black holes. The observations carried out by Kormendy and Bender indicate that this must indeed be the dominant process of black hole formation and growth.
So watch out next time you decide to play games in the dark… You might just get eaten instead of… ahem… tagged.
Original Story Source: Max-Planck-Institut / Image: wikisky.org. We thank you so much!
