Universe Today

The bright red spots at the edge of the Pinwheel Galaxy means bad news for life. Image credit: NASA/JPL-Caltech/STScI

The Pinwheel Galaxy is also known as Messier 101. This galaxy was first discovered in 1781 by astronomer Pierre Mechain. He then dubbed it a nebula. However we now know that unlike a nebula, which is the cloud of gas from which new stars are born, it was actually a galaxy. This would not be discovered until the 20th century when astronomer Erwin Hubble discovered the existence of other galaxies beyond the Milky Way.

The Pinwheel Galaxy is one of the largest Galaxies yet discovered. At a whopping 170,000 light years in diameter it is nearly double the size of the Milky Way Galaxy. The Pinwheel galaxy has a structure similar to that of the Milky Way being a spiral galaxy. This is a galaxy with with center with arms extending out in a spiral. The Pinwheel galaxy is also massive it is believed to have a mass that is the equivalent of over 100 billion solar systems in its main disk and and 3 billion solar systems in its smaller bulge. If you would want to visit this galaxy unfortunately, it would not be as close as you hoped. The estimates on its distance from the Milky Way is anywhere between 20 million to 26 million light years.

The pinwheel galaxy proved to be a significant discovery in astronomy. Thanks to the observation of it and other galaxies we are learning more about how our own galaxy is formed and what makes life possible in a galaxy. For example, astronomers are now able to observe distant galaxies like the Pinwheel galaxy and learn whether a galaxy has elements such as carbon that can sustain life.

We are learning more about the other galaxies as the technology to observe them improves. We can get to learn even more about the composition of galaxies and even if life already exists. This may be the biggest contribution to science that can come from observing galaxies like the Pinwheel galaxy.

If you enjoyed this article there are several others on Universe Today that you will enjoy. There is a great article about Hubble and his discoveries. There is also an interesting article on the furthest galaxy yet found.

There are also some interesting resources about the Pinwheel galaxy online. There is a great page on the Pinwheel galaxy on the SEDS Messier web site. There is also an article about the Pinwheel Galaxy on NASA'S Hubble web page.

You can also check out Astronomy Cast. Episode 97 talks about Galaxies.

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Examples of ring objects (Mizuno et al./Spitzer)

Three-color images of four objects. Red: 24 μm, green: 8 μm, blue: 3.6 μm (Mizuno et al./Spitzer)

Oh, and also because Don Mizuno and co-authors may have found two, quite local, spiral galaxies that no one has ever seen before!
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Stars wandering outside the galactic plane of the Milky Way could number in the billions. Image Credit: APOD

The Milky Way is the galaxy that are our Solar system to resides in. It is also the very first galaxy that astronomers were aware of. The word galaxy gets its name from the Greek Galaxios which means milky circle. This refers to the band of light that is visible in the night sky. This is the visible portion of the Milky Way galaxy that we can see from Earth. It has been observed by several cultures and though to have many meanings. For example the Mayans thought that the Milky way was a celestial path that lead to the underworld.

The Milky Way Galaxy is a spiral galaxy. This type of galaxy has a center with arms of clustered stars spiraling out. The Milky Way Galaxy is estimated to have anywhere from 200 billion to 400 billion stars. If that does not give you an idea of how big it is, the Milky Way is roughly 100,000 light years in diameter. That basically means if we even had the technology to traverse it at the speed of light it would take hundreds of generations to travel across the Milky Way. Another interesting feature is that the Milky way seems to have a massive black hole at the center that is several times greater than most observed in space.

The Milky Way was considered to be a celestial phenomenon, but few astronomers realized that it was actually composed of distant stars. This was because the ancient astronomers believed the stars where fixed on a celestial sphere that surrounded the Earth. This lead philosophers like Aristotle to believe that the Milky Way was actually the result of the ether between the stars being ignited. However the ancient philosopher Democritus ,the first person to theorize the existence of the atom, made a more accurate guess. He proposed that the Milky Way was actually a cluster of distant stars. This was the first discovery of a galaxy and the hint that the universe was much larger than originally thought. Further observations with improved telescopes helped to confirm these ancient findings. Astronomer Edwin Hubble not only confirmed the existence of the Milky Way but also of other galaxies.

There are still many mysteries about the Milky Way and other galaxies that have not been explained. For instance, the Milky Way and its fellow galaxies are more massive than they appear. Astrophysicists have determined that this means there is a type of matter not observable under any currently known form of radiation. Hopefully future research should reveal more about this unique type of matter.

If you enjoyed this article there are several others on Universe Today that you will enjoy. There is a great article about Edwin Hubble and his discoveries. You can also learn more about Democritus and his work on the atom.

There are also many great resources online that you can use to learn more about the Milky Way. There is a great article about the structure of the Milky Way on the University of California San Diego Astrophysics website. you can also check out the Milky Way page on the University Corporation for Atmospheric Research website.

You can also listen to Astronomy Cast. Episode 99 is about the Milky Way.

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This image created from data taken from both the NASA/ESA Hubble Space Telescope and the Sloan Digital Sky Survey demonstrates that the Hubble sequence six billion years ago was very different from the one that astronomers see today. Credit: NASA, ESA, Sloan Digital Sky Survey, R. Delgado-Serrano and F. Hammer (Observatoire de Paris)

Galaxies come in all sorts of shapes. But in the past, the various galaxy shapes used to be more diverse and "peculiar" than they are now. Over time, according to a new study, galaxies tend to become spirals. "Six billion years ago, there were many more peculiar galaxies than now — a very surprising result," said Rodney Delgado-Serrano, lead author of a new paper. "This means that in the last six billion years, these peculiar galaxies must have become normal spirals, giving us a more dramatic picture of the recent Universe than we had before."
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The Milky Way is our home, but it's really just one galaxy in a Universe filled with galaxies. Each one with hundreds of billions of stars. Some can even have a trillion stars or more. Here are some amazing galaxy photos.

This is an image of M82, also known as the Cigar Galaxy, because that's how it looks in many astrophotos. Astronomers have known that this galaxy has regions of intense star formation, but this image from NASA's Spitzer Space Telescope enables astronomers to peer through the obscuring dust that block the star forming regions.

Here's an image of the irregular galaxy NGC 1569 taken by the Hubble Space Telescope. We love to see the grand spiral galaxies, like our own Milky Way, but smaller, irregular galaxies like this are more common in the Universe. They're the building blocks of larger galaxies, merging together to form larger and larger galaxies.

If we could travel a few million light-years away from the Milky Way and then look back, this is what we'd see. This is the spiral galaxy NGC 7331; a virtual twin of our own home galaxy. NGC 7331 is located in the Pegasus constellation, about 50 million light-years from Earth.

Here's an image of one of the youngest galaxies ever seen; I Zwicky 18. Astronomers think this galaxy only got going about 500 million years ago, when it collapsed out of a cloud of gas and dust. It's believed to have gone through its most recent burst of star formation about 4 million years ago.

This is an image of the Pinwheel Galaxy, also known as M101. In this infrared image captured by NASA's Spitzer Space Telescope, you can see regions of active star formation in the galaxy.

We've written many articles about galaxies for Universe Today. Here's an article about how many galaxies there are in the Universe, and here's an article about how galaxies lose their gas.

If you'd like more info on galaxies, check out NASA's World Book on Galaxies, and here's NASA's Science Page on Galaxies.

We've also recorded an episode of Astronomy Cast about galaxies. Listen here, Episode 97: Galaxies.

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NGC 2976.. NASA, ESA, and J. Dalcanton and B. Williams (University of Washington, Seattle)

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Caption: A figure illustrating the Hubble sequence. Image: Ville Koistinen

One look at a Hubble Deep Field image reveals that galaxies come in all sorts of shapes and sizes. But why? Astronomers have been at a loss to explain the diversity of galaxy shapes seen in the Universe. But now, two astronomers have tracked the evolution of galaxies over thirteen billion years from the early Universe to the present day, helping to clarify the "Hubble Sequence," a classification of galaxies developed by Edwin Hubble. Keys to their model include galaxy mergers and dark energy.
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Arp 192 from his publication (left) compared to SDSS image (right). Prominent jet in upper right is present in Arp's image is missing from modern images.

During the “Great Debate” of 1920 astronomers Herber Curtis and Harlow Shapley had a famous debate on the nature of “spiral nebulae”. Curtis argued they were “island universes” or what we would today call a galaxy. Shapley was of the opinion that they were spiral structures within our own galaxy. One of the evidences Shapley put forth was that another astronomer, Adriaan vanMaanen, had reported detecting rotation of these objects over a period of years leading to an overall rotation rate of ~10⁵ years. If these spiral nebulae were truly as far (and thus, as large) as Curtis suggested this would mean they would be rotating well beyond the speed of light at their outer edges.

It was later determined vanMaanen's rotation was a case of wishful thinking when Hubble eventually determined the true distance to the Andromeda galaxy. From then on, it was well established that galaxies are so large, their motions will not be observed in human lifetimes. Aside from local flare ups of supernovae and other such events, galaxies should be relatively static. Yet in just over 40 years, a distinct, large-scale feature in the galaxy NGC 3303 seems to have disappeared entirely. Read more…

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Spiral galaxies are undoubtedly one of the most beautiful structures in the universe. Yet, their simple elegance belies a complex nature. How do such structures not "wind up" and what causes them in the first place? The answers to these questions is a long standing challenge. Under one model, spiral structure is created by spiral density waves. In another, they are induced by tidal interactions. It is this approach that is explored in a new paper by Dobbs et al., accepted for publication in the Monthly Notices of the Royal Astronomical Society. Specifically, the authors attempted to use modeling of tidal forces to recreate the structure of the spiral arms on the grand design spiral, M51. Read more…

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Hubble's latest image is another stunner — and just look at all the galaxies! Hubble has produced a new version of the Ultra Deep Field, this time in near-infrared light and taken with the newly installed Wide Field Camera 3. This is the deepest image yet of the Universe in near-infrared, and so the faintest and reddest objects in the image are likely the oldest galaxies ever identified, and they likely formed only 600–900 million years after the Big Bang. This image was taken in the same region as the visible Ultra Deep Field in 2004, but this new deep view at longer wavelengths provides insights into how galaxies grew in their formative years early in the Universe's history.
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As galaxies evolve, many lose their gas. But how they do this is a point of contention. One possibility is that it is used to form stars when the galaxies undergo intense periods of star formation known as starburst. Another is that when large galaxies collide, the stars pass through one another but the gas gets left behind. It's also possible that the gas is pulled out in close passes to other galaxies through tidal forces. Yet another possibility involves a wind blowing the gas out as galaxies plunge through the thin intergalactic medium in clusters through a process known as ram pressure.

A new paper lends fresh evidence to one of these hypotheses. Read more…

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Peering Deeper Into the Core of M87: At top left, a VLA image of the galaxy shows the radio-emitting jets at a scale of about 200,000 light-years. Subsequent zooms progress closer into the galaxy's core, where the supermassive black hole resides. In the artist's conception (background). the black hole illustrated at the center is about twice the size of our Solar System, a tiny fraction of the size of the galaxy, but holding some six billion times the mass of the Sun. Credit: Bill Saxton, NRAO/AUI/NSF

Where to find a SMBH? In the nucleus of a galaxy! In fact, it seems that all spiral galaxies with bulges, and all elliptical galaxies (except, perhaps, dwarf ellipticals) have a super massive black hole at the center of their nuclei (and some may have two).

How to 'weigh' a SMBH? There are two techniques – for our own galaxy, observe stars in orbit around the SMBH (which is SgrA*), apply the equations of orbital mechanics (Kepler's laws will do), turn the handle (that means 'do the calculations'), and out comes an estimate of the SMBH's mass. For other galaxies, take a spectrum of the nucleus, estimate the line of sight velocity of the stars (or gas), work out how it changes across the very center, apply equations derived from Newtonian mechanics and gravitation (you could use general relativity, but Newton is good enough), turn the handle, and … (as above).

When a super massive black hole eats (i.e. when matter falls into it), an accretion disc forms around it (conservation of angular momentum) – which emits enormous quantities of electromagnetic radiation – and a pair of jets emerge in the directions of the poles (of course nothing comes from the SMBH itself; matter is funneled into the jets by mechanisms that are not yet well understood). Now you have an active galactic nucleus (AGN), and, if it's particularly active, a quasar (or, if you are looking right down the barrel of the jet, a blazar).

Super massive black holes are part of every astronomy course, it seems; Supermassive Black Holes, for example, is part of a University of Tennessee course. NASA's World Book has an entry on super massive black holes, as does Cornell University's Ask an Astronomer.

Universe Today has many articles on super massive black holes; here are a few: Astronomers Find Most Distant Supermassive Black Hole Yet, Greedy Supermassive Black Holes Dislike Dark Matter, Super-Supermassive Black Hole, and Supermassive Black Hole Mashes Up and Consumes Star.

There are two Astronomy Cast episodes of particular interest to this topic: Black Holes Big and Small, and Quasars.

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Here's your chance to play online slot machines without risking your life savings. Plus it's an opportunity to contribute to a citizen science project that is sure to revolutionize our understanding of galaxy mergers. Galaxy Zoo's newest project asks for help in looking at colliding galaxies, and uses a tool akin to a cosmic slot machine to compare images of galactic pile-ups with millions of simulated mergers.

"The analogy I've been using is that it is like driving past a car crash," said Galaxy Zoo team member Chris Lintott from Oxford University. "You get a snapshot of the action, but there are two things you want to know: what caused the crash (or what did things look like before it all went wrong), and you want to know what the outcome is going to be. We're doing the same thing. We want to know what the galaxies looked like before the mergers started disrupting them, and we want to know how they are going to end up. Just like our other Galaxy Zoo projects, humans are much better at doing this than computers, and lots of humans are even better."
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Looking at a galaxy edge-on provides astronomers the opportunity to study different aspects of galaxies than a face-on view offers. This Hubble image of NGC 4710 is part of a survey conducted to provide more information about the puzzling bulges that form around the middle of some galaxies. Have these galaxies been "eating" too much, or is it just part of a "middle-age spread" similar to what humans experience? Astronomers aren't sure why bulges evolve and become a substantial component of most spiral galaxies.
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This 3D illustration shows the position of the galaxies and reveals the extent of this gigantic structure. The galaxies located in the newly discovered structure are shown in red. Galaxies that are either in front or behind the structure are shown in blue. Credit: ESO

Are there "skeletons" out in the Universe –structures that form the framework of how galaxies are distributed? Astronomers have tracked down a gigantic, previously unknown assembly of galaxies located almost seven billion light-years away from us, which seems to point to a prominent galaxy structure in the distant Universe, providing further insight into the cosmic web and how it formed. “Matter is not distributed uniformly in the Universe,” says Masayuki Tanaka from ESO, who led the new study. “In our cosmic vicinity, stars form in galaxies and galaxies usually form groups and clusters of galaxies. The most widely accepted cosmological theories predict that matter also clumps on a larger scale in the so-called ‘cosmic web’, in which galaxies, embedded in filaments stretching between voids, create a gigantic wispy structure.”
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