Even after thirty years of faithful service, the Hubble Space Telescope continues to reveal truly fascinating things about our Universe. This includes the image (shown at top) taken of the astronomical feature known as NGC 2273, a barred spiral galaxy similar to the Milky Way. However, upon closer inspection, the image reveals that the spiral arms of this galaxy contain a second set of spiral arms.Continue reading “Hubble Sees a Galaxy With Spiral Arms, Surrounded by Other Spiral Arms”
With only an introductory course in science, it’s easy to think that scientists strictly follow the scientific method. They propose a new hypothesis, test that hypothesis, and after many years of hard work, either confirm or reject it. But science is often prone to chance. And when a surprise presents itself, the book titled “Scientific Method 101” often gets dropped in the trash. In short, science needs — and perhaps thrives on — stupid luck.
Take any scientific mission. Often designed to do one thing, a mission tends to open up a remarkable window on something unexpected. Now, NASA’s Kepler space telescope, designed to hunt for planets in our own galaxy, has helped measure an object much more distant and more massive than any of its detected planets: a black hole.
KA1858+4850 is a Seyfert galaxy with an active supermassive black hole feeding on nearby gas. It lies between the constellations Cygnus and Lyra approximately 100 million light-years away.
In 2012, Kepler provided a highly accurate light curve of the galaxy. But the team, led by Liuyi Pei from the University of California, Irvine, also relied on ground-based observations to compliment the Kepler data.
The trick is to look at how the galaxy’s light varies over time. The light first emitted from the accretion disk travels some distance before reaching a gas cloud, where it’s absorbed and re-emitted a short time later.
Measuring the time-delay between the two emitted points of light tells the size of the gap between the accretion disk and the gas cloud. And measuring the width of the emitted light from the gas cloud tells the velocity of the gas moving near the black hole (due to an effect known as Doppler broadening). Together, these two measurements allow astronomers to determine the mass of the supermassive black hole.
Pei and her colleagues measured a time delay of roughly 13 days, and a velocity of 770 kilometers per second. This allowed them to calculate a central black hole mass of roughly 8.06 million times the mass of the Sun.
The results have been published in the Astrophysical Journal and are available online.
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Discovered on October 29, 1780 by Pierre Mechain, this active Seyfert galaxy is magnificent to behold in amateur equipment and even more so in NASA/ESA Hubble Space Telescope photographs. Located in the constellation of Cetus and positioned about 45 million light years away, this spiral galaxy has a claim to fame not only for being strong in star formation, but as one of the most studied galaxies of its type. Cutting across its face are red hued pockets of gas where new suns are being born and dark dustlanes twist around its powerful nucleus.
When Mechain first observed this incredible visage, he mistook it for a nebula and Messier looked at it, but did not record it. (However, do not fault Messier for lack of interest at this time. His wife and newly born son had just died and he was mourning.) In 1783, Sir William Herschel saw it as an “Ill defined star surrounded by nebulousity.” but would change his tune some 8 years later when he reported: “A kind of much magnified stellar cluster; it contains some bright stars in the centre.” His son, John Herschel, would go on to catalog it – not being very descriptive either.
This video zooms in on spiral galaxy Messier 77. The sequence begins with a view of the night sky near the constellation of Cetus. It then zooms through observations from the Digitized Sky Survey 2, and ends with a view of the galaxy obtained by Hubble. Credit:NASA, ESA, Digitized Sky Survey 2. Acknowledgement: A. van der Hoeven
At almost double the size of the Milky Way, we now know it is a barred spiral galaxy. According to spectral analysis, Messier 77 has very broad emission lines, indicating that giant gas clouds are rapidly moving out of this galaxy’s core, at several hundreds of kilometers per second. This makes M77 a Seyfert Type II galaxy – one with an expanding core of starbirth. In itself, that’s quite unique considering the amount of energy needed to expand at that rate and further investigations found a 12 light-year diameter, point-like radio source at its core enveloped in a 100 light year swath of interstellar matter. A miniature quasar? Perhaps… But whatever it is has a measurement of 15 million solar masses!
Deep at its heart, Messier 77 is beating out huge amounts of radiation – radiation suspected to be from an intensely active black hole. Here the “galaxy stuff” is constantly being drawn towards the center, heating and lighting up the frequencies. Just this area alone can shine tens of thousands of times brighter than most galaxies… but is there anything else hiding there?
“Active galactic nuclei (AGNs) display many energetic phenomena—broad emission lines, X-rays, relativistic jets, radio lobes – originating from matter falling onto a supermassive black hole. It is widely accepted that orientation effects play a major role in explaining the observational appearance of AGNs.” says W. Jaffe (et al). “Seen from certain directions, circum-nuclear dust clouds would block our view of the central powerhouse. Indirect evidence suggests that the dust clouds form a parsec-sized torus-shaped distribution. This explanation, however, remains unproved, as even the largest telescopes have not been able to resolve the dust structures.”
Before you leave, look again. Clustered about Messier 77’s spiral arms are deep red pockets – a sign of newly forming stars. Inside the ruby regions, neophyte stars are ionising the gas. The dust lanes also appear crimson as well – a phenomenon called “reddening” – where the dust absorbs the blue light and highlights the ruddy color. A version of this image won second place in the Hubble’s Hidden Treasures Image Processing Competition, entered by contestant Andre van der Hoeven.
Twistin’ the night away…
Nearly four million light years away in the direction of the constellation of Canes Venatici, a visage of creation awaited to be revealed. Now, thanks to the teamwork of the astronomical image processors at the Space Telescope Science Institute in Baltimore, Maryland, and world-renowned astrophotographers Robert Gendler and Jay GaBany, we’re able to see combined Hubble Space Telescope data with ground-based telescope imaging. Let’s look deep into spiral galaxy, Messier 106.
This wasn’t an overnight imaging project. “A few months ago the Hubble Heritage Team contacted me and asked if I’d be interested in making a large format image of M106 from the available data on the Hubble Legacy Archive,” says Gendler. “I agreed and went to work downloading a large number of data sets from the HLA. I realized this would be a massive project. The image would be a mosaic of more than 30 panels and would incorporate both wideband and narrowband data sets.”
With the cooperation of Jay GaBany, they combined their own observations/images of this magnificent structure and compiled it with Hubble data – filling in areas where no data was available. The resulting image is a portrait of such depth and beauty that it’s almost like looking into the eyes of creation itself.
Be swept away…
If you’re drawn to the core of Messier 106, there’s good reason. It isn’t just an ordinary spiral galaxy, it’s one that has a peculiar jet flow which can be detected in radio and in H-alpha wavelengths. “Due to the special geometry of the galaxy, the jets emerge from the nuclear region through the galactic disk,” says Marita Krause (et al). “Also the distribution of molecular gas looks different from that in other spiral galaxies.” It is just this difference that makes NGC 4258 (M106) stand out a bit from the crowd and so worthy of further processing. According to new modeling techniques the “concentration of CO along the ridges is due to interaction of the rotating gas clouds with the jet’s magnetic field by ambipolar diffusion. This magnetic interaction is thought to increase the time the molecular clouds reside near the jet thus leading to the quasi-static CO ridge.”
Knowing those jets are present and the hunger to reveal them through imaging became the driving force for R. Jay GaBany. “Since the early 1960s, M106, also known as NGC 4258, has been known to exhibit an extra pair of arms, located between the spiral arms comprised of stars, dust and gas. But an explanation for their existence remained elusive until earlier in this decade,” says Jay. “My contribution to the image came from my 2010 image of M-106 that revealed the full extent of its amazing jets. My image include 22 hours of white light exposures through clear, red, blue and green filters plus and other 15 hours of imaging through a 6nm narrow band h-alpha filter.”
“Seen in the light emitted by hydrogen molecules when they become ionized, these arms display an artificial red hue to make them visible in the image I produced. The extra arms are now believed to be caused by high energy jets emanating from an active 40 million solar mass super-massive black hole menacing the galaxy’s center,” explains GaBany. “Because the jets are tilted at a low inclination they pierce the disk and surrounding halo of this galaxy. So, as the jets pass through regions of gas, they create an expanding cocoon of shock waves that heats the surrounding material causing it to release radiation in optical wavelengths. The curvature and fraying seen at their extremities represents previous trajectories of the jet due to past precession. Precession is a change in the orientation of the rotation axis of a spinning object. For example, the wobble of a spinning top.”
Yet, that’s not all. This low luminosity Seyfert II galaxy is also hosting a maser – its warped disk of water molecules discovered in 1994. Through radio observations, M106 became the first of its kind to show the exact location of the core of an AGN (active galactic nucleus). According to a study done by JR Herrnstein (et al): “NGC 4258 is an exceptional laboratory for the study of AGN accretion processes. The nuclear maser reveals details about the kinematics and structure of the accretion disk on subparsec scales and permits the determination of the central mass with great precision.”
And there is still more…
Deep inside lurks that known supermassive black hole – one that’s extremely active and produces bright microwave radiation. But, don’t stop there. Ordinarily a spiral galaxy has two arms, but M106 has double. These ethereal “extras” can be seen as faint ribbons of gas at optical wavelengths, but become solidified when viewed in x-ray and radio. Here the structure is formed in hot gas rather than stars. While this process was once a mystery to astronomers, new information suggests they may arise from the black hole activity, making them a unique artifact. What could cause it? These “extra arms” could be the result of the violent turbulence at the core – where gases are superheated and interact with their denser counterparts causing them to illuminate. At the perimeter of the galactic structure, the gases are more loose and the arching formation could be the product of the movement of jet activity.
“One goal I had early on was to feature the well known ‘anomalous arms’ of M106,” said Gendler. “This feature, peculiar to M106, is thought to arise from superheated gases, energized by accretion of matter into the galaxy’s massive black hole. The anomalous arms emit light in the visual spectrum around 656nm (hydrogen alpha) and I found a fair amount of hydrogen alpha data sets for the arms in the HLA.”
Gendler was responsible for all the image assembly and processing. “Assembling the image required over two months,” he said. “The quality of the data ranged from good to very poor. The central galaxy had sufficient color data but away from the center the Hubble data was incomplete and in some areas did not exist. I then decided to use ground based data from my own image and Jay GaBany’s image of M106 to fill in areas of missing or incomplete Hubble data. I also used ground based data to boost the signal of the outer areas of the galaxy as the Hubble data was sparse and of short exposure for the more remote areas of the galaxy.”
All in all, Messier 106 is a galaxy that deserves attention – attention and a loving touch given by two of the very best amateur astronomers and dedicated astrophotographers to be found.
Original News Source: HubbleSite Image Release.