New Insights on How Spiral Galaxies Get Their Arms

Spiral galaxies are some of the most beautiful and photogenic residents of the universe. Our own Milky Way is a spiral. Our solar system and Earth reside somewhere near one of its filamentous arms. And nearly 70 percent of the galaxies closest to the Milky Way are spirals.

But despite their common shape, how galaxies like ours get and maintain their characteristic arms has proved to be an enduring puzzle in astrophysics. How do the arms of spiral galaxies arise? Do they change or come and go over time?

Read More.

(Source: christinetheastrophysicist)

The winners and notable photos of the 4th International Earth and Sky Photo Contest, a program by The World at Night (TWAN) in collaboration with the Global Astronomy Month and the National Optical Astronomy Observatory (NOAO). The contest theme is Dark Skies Importance. Similar to TWAN itself, the contest also aims to reclaim the natural beauty of starry sky and to help preserving the dark skies which are not yet dominated by artificial lights.

The images in this video are copyrighted by the photographers. Feel free to share the video (embedding or sharing the link) to promote the contest in non-commercial way. Permission is needed from TWAN (info@twanight.org) for any other use. The music is by sound artist Thomas Nordwest (thomasnordwest.com). Winner photos and more information on the contest page: twanight.org/contest

via Babak Tafreshi and Astronomers Without Borders

Light Pollution | Losing The Dark

Starry skies are a vanishing treasure because light pollution is washing away our view of the cosmos. It not only threatens astronomy, it disrupts wildlife, and affects human health. The yellow glows over cities and towns — seen so clearly from space — are testament to the billions spent in wasted energy from lighting up the sky.

To help raise public awareness of some of the issues pertaining to light pollution, Loch Ness Productions in collaboration with the International Dark-Sky Association has created a 6.5-minute “public service announcement” called Losing the Dark. It introduces and illustrates some of the issues regarding light pollution, and suggests three simple actions people can take to help mitigate it.

Losing the Dark was initially created in fulldome video format for digital planetarium use. It also has been made as a conventional flat screen video, for use in classrooms, kiosks, museum theaters, and advocate multimedia presentations. Classic planetarium theaters without fulldome capability can show this version using their traditional video projectors.

via The International Dark Sky Association (IntlDarkSkyAssoc)

Stay Curious! Watch: The City Dark; more about the film HERE.

Galactic Habitable Zone

One of our Sun’s unusual features is its orbit around the center of the galaxy, which is significantly less elliptical (“eccentric”) than those of other stars similar in age (and therefore metallicity, or proportion of an object’s chemical composition other than hydrogen and helium) and type and is barely inclined relative to the Galactic plane. This circularity in the Sun’s orbit prevents it from plunging into the inner Galaxy where life-threatening supernovae are more common. Moreover, the small inclination to the galactic plane avoids abrupt crossings of the plane that would stir up the Sun’s Oort Cloud and bombard the Earth with life-threatening comets.

In fact, the Sun is orbiting very close to the “co-rotation radius” of the galaxy, where the angular speed of the galaxy’s spiral arms matches that of the stars within. As a result, the Sun avoids crossing the spiral arms very often, which would expose Earth to supernovae that are more common there. These exceptional circumstances may have made it more likely for complex life and human intelligence to emerge on Earth. According to Guillermo Gonzalez (an astronomer at Iowa State University), fewer than five percent of all stars in the galaxy enjoy such a life-enhancing galactic orbit. Other astronomers point out, however, that many nearby stars move with the Sun in a similar galactic orbit.

The Sun resides in a pancake region of the Galaxy called the “disk” with a strong concentration of stars (and gas and dust) within 3,000 light-years (ly) of the galactic plane, which includes the so-called “thin disk” that has more relatively younger stars within 1,500 ly of the plane (more on stellar population groups in our Milky Way Galaxy). This region contains relatively young to intermediate-aged stars that within around five billion years old with relatively higher average metallicity than other galactic regions located outside of the galactic core, in a circular band that broadens with time. Generated by the deaths of older stars, the greater availability of elements higher than hydrogen and helium in this galactic region favor the formation of rocky inner planets as large as Earth, or bigger (Gonzalez et al, 2001). Moreover, the galactic orbits of stars in this region tend to be relatively circular — with low to moderate eccentricity. According to one recent definition of the galactic habitable zone, as much as 10 percent of all stars in the Milky Way may have experienced chemical and environmental conditions suitable for the development of complex Earth-type life over the past eight to four billion years for evolutionary development (press release; and Lineweaver et al, 2004, in pdf). (Further discussion of the different galactic regions and their distinctive stellar populations is available from ChView’s “The Stars of the Milky Way.”)

In recent millenia, the Sun has been passing through a Local Interstellar Cloud (LIC) that is flowing away from the Scorpius-Centaurus Association of young stars dominated by extremely hot and bright O and B spectral types, many of which will end their brief lives violently as supernovae. The LIC is itself surrounded by a larger, lower density cavity in the interstellar medium (ISM) called the Local Bubble, that was probably formed by one or more relatively recent supernova explosions. As shown in a 2002 Astronomy Picture of the Day, located just outside the Local Bubble are: high-density molecular clouds such as the Aquila Rift which surrounds some star forming regions; the Gum Nebula, a region of hot ionized hydrogen gas which includes the Vela Supernova Remnant, which is expanding to create fragmented shells of material like the LIC; and the Orion Shell and Orion Association, which includes the Great Orion Nebula, the Trapezium of hot B- and O-type stars, the three belt stars of Orion, and local blue supergiant star Rigel.

Top Image credit: Yeshe Fenner, STcI, AURA, NASA, ESA

(Source: stellar-indulgence, via atomstargazer)

Nightscapes from Real de Catorce, México — César Cantú

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Milky Way’s Black Hole Munches On Supercooked Gas

It’s a simple menu, but smoking hot. The black hole at the center of the Milky Way galaxy is sucking in ultra-hot molecular gas, as seen through the eyes of the Herschel space telescope.

“The biggest surprise was quite how hot the molecular gas in the innermost central region of the galaxy gets. At least some of it is around 1000ºC [1832º F], much hotter than typical interstellar clouds, which are usually only a few tens of degrees above the –273ºC [-460ºF] of absolute zero,” stated the European Space Agency.

Herschel, which is out of coolant and winding down its scientific operations, will continue producing results in the next few years as scientists crunch the results. The telescope has found a bunch of basic molecules in the Milky Way that include water vapour and carbon monoxide, and has been engaged in looking to learn more about the gas that surrounds the massive black hole at our galaxy’s center.

In a region called Sagittarius* (Sgr A*), this huge black hole — four million times the mass of the sun — is thankfully a safe distance from Earth. It’s 26,000 light years away from the solar system.

Trouble is, there’s a heckuva lot of dust blocking our view to the center of the galaxy. Herschel got around that problem by taking pictures in the far-infrared, seeking heat signatures that can bely intense activity in and around the black hole.

“Herschel has resolved the far-infrared emission within just 1 light-year of the black hole, making it possible for the first time at these wavelengths to separate emission due to the central cavity from that of the surrounding dense molecular disc,” stated Javier Goicoechea of the Centro de Astrobiología, Spain, lead author of a paper reporting the results.

The science team supposes that there are strong shocks within the gas (which is magnetized) that help turn up the heat. The shocks could occur when gas clouds butt up against each other, or material shoots out Fast and Furious-style between stars and protostars (young stars.)

“The observations are also consistent with streamers of hot gas speeding towards Sgr A*, falling towards the very center of the galaxy,” stated Goicoechea. “Our galaxy’s black hole may be cooking its dinner right in front of Herschel’s eyes.”

image 1: Artist’s concept of a supermassive black hole at the center of a galaxy. credit: NASA/JPL-Caltech

image 2: At left, ionized gas in the galaxy as seen in radio wavelengths; at right, the spectrum at the center seen by Herschel. credit: Radio-wavelength image: National Radio Astronomy Observatory/Very Large Array (courtesy of C. Lang); spectrum: ESA/Herschel/PACS & SPIRE/J.R. Goicoechea et al. (2013).

Galaxy Cove Vista

(Source: thenewenlightenmentage, via thenewenlightenmentage)

Stellar Archaeology Traces Milky Way’s History

Unfortunately, stars don’t have birth certificates. So, astronomers have a tough time figuring out their ages. Knowing a star’s age is critical for understanding how our Milky Way galaxy built itself up over billions of years from smaller galaxies. But Jason Kalirai of the Space Telescope Science Institute and The Johns Hopkins University’s Center for Astrophysical Sciences, both in Baltimore, Md., has found the next best thing to a star’s birth certificate.

Using a new technique, Kalirai probed the burned-out relics of Sun-like stars, called white dwarfs, in the inner region of our Milky Way galaxy’s halo. The halo is a spherical cloud of stars surrounding our galaxy’s disk. Those stars, his study reveals, are 11.5 billion years old, younger than the first generation of Milky Way stars. They formed more than 2 billion years after the birth of the universe 13.7 billion years ago. Previous age estimates, based on analyzing normal stars in the inner halo, ranged from 10 billion to 14 billion years. Kalirai’s study reinforces the emerging view that our galaxy’s halo is composed of a layer-cake structure that formed in stages over billions of years.

White dwarf stars have remarkable properties, yet they are very simple. These stripped cores of normal hydrogen-burning stars are about 1 million times denser than matter on Earth. This means that a tablespoon of material from a white dwarf’s surface would weigh as much as a school bus on Earth. White dwarfs also have no fuel to generate energy, and most of their atmospheres contain a single atom, hydrogen.

The second figure illustrates the spectral features of a white dwarf, in comparison to the Sun and a blue giant. The white dwarf spectrum is simple, containing only absorption lines from the hydrogen atom. But, unlike the same lines in the blue giant spectrum (a bloated star with a low density), the features in the white dwarf are broadened due to the intense pressure on the surface of the star (essentially, the energy levels of the atom are being perturbed). This broadening of the lines, as well as their depth, is directly related to the mass and temperature of the star. Unlike for most stars, astronomers can therefore reliably establish fundamental properties for white dwarfs from their spectra.

Credit: NASA, ESA, and A. Feild and J. Kalirai (STScI)

(Source: stellar-indulgence)

The Astronomer’s League by Mike Gottschalk

Calling Anyone by Larry Landolfi
A giant parabolic radio dish antenna in Ft. Davis, Texas, belonging to the National Radio Astronomy Observatory (NRAO), looking into the summer Milky Way in this composite photo.

(Source: thedemon-hauntedworld)

“When a massive power outage struck southern California in the 1990s, Los Angeles residents reportedly called 911 to express alarm about strange clouds hovering overhead; they were seeing the Milky Way for the first time.”
— Seeing in the Dark | Light Pollution

[image source]

(Source: eddyizm)

Monument Rocks and the Way by Scott Ackerman Photography on Flickr.

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Extreme Galaxy Observed Forming Stars 100 Times the Rate of the Milky Way

The tiny red spot in the image above is one of the most efficient star-making galaxies ever observed, converting gas into stars at the maximum possible rate.

The galaxy is shown here in an image from NASA’s Wide-field Infrared Survey Explorer (WISE), which first spotted the rare galaxy in infrared light. Visible-light observations from NASA’s Hubble Space Telescope (inset) reveal that the starlight in this galaxy is extraordinarily compact, with most of the light emitted by a region just a fraction of the size of the Milky Way galaxy. Within that tiny region, stars are forming at a rate hundreds of times that of our galaxy. 

The galaxy, called SDSSJ1506+54, jumped out at the researchers when they looked at it using data from WISE’s all-sky infrared survey. Infrared light is pouring out of the galaxy, equivalent to more than a thousand billion times the energy of our sun.

“Galaxies burn gas like a car engine burns fuel. Most galaxies have fairly inefficient engines, meaning they form stars from their stellar fuel tanks far below the maximum theoretical rate,” said Jim Geach of McGill University, lead author of a new study appearing in the Astrophysical Journal Letters. “This galaxy is like a highly tuned sports car, converting gas to stars at the most efficient rate thought to be possible,” he said.

Hubble’s visible-light observations revealed that the galaxy is extremely compact, with most of its light emanating from a region just a few hundred light-years across.

“This galaxy is forming stars at a rate hundreds of times faster than our Milky Way galaxy, but the sharp vision of Hubble revealed that the majority of the galaxy’s starlight is being emitted by a region just a few percent of the diameter of the Milky Way. This is star formation at its most extreme,” said Geach.

Why is SDSSJ1506+54 so unusual? Astronomers say they’re catching the galaxy in a short-lived phase of evolution, possibly triggered by the merging of two galaxies into one. The star-formation is so ferocious that in a few tens of millions of years, the blink of an eye in a galaxy’s life, the gas will be used up, and the galaxy will mature into a massive elliptical galaxy.

 Article - Sources

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the-science-llama:

Our Night Sky When We Collide With Andromeda

In the photos above in order:

— Present day
— 2 Billion years from now the of the approaching Andromeda galaxy is noticeably larger
— 3.75 Billion years, Andromeda fills the field of view
— 3.85 Billion years, the sky is ablaze with new star formation
— 3.9 Billion years, star formation continues
— 4 Billion years, Milky Way is warped and Andromeda is tidally stretched
— 5.1 Billion years, cores of both galaxies appear as a pair of globes
— 7 Billion years, the cores have merged, the bright core dominates the night sky

Here is an animation of the collision

In around 4 billion years our galaxy, The Milky Way, will collide with our neighbor galaxy Andromeda or M31. You might think this will be a catastrophic event for everything in the galaxy including our solar system but in reality most of the solar systems will simply pass by each other. However, given the new galactic center and the new mass pulling everything towards it and tossing it around, the orbits of those solar systems will be changed.

The massive Andromeda galaxy is about 120,000 light years across while our galaxy is 100,000 light years across. Given their size, the speed that we our hurdling towards each other is relatively small at 250,000 miles per hour.

Sources:
http://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html
http://www.nasa.gov/multimedia/imagegallery/image_feature_1837.html