ESO: Dustfree dwarf galaxy provides lessons on cosmic distances

ESO (European Southern Oberservatory) has a new report out:

The Milky Way’s Clean and Tidy Galactic Neighbour

This image, captured with the OmegaCAM camera on ESO’s VLT Survey Telescope in Chile, shows an unusually clean small galaxy. IC 1613 contains very little cosmic dust, allowing astronomers to explore its contents with great clarity.
This image, captured with the OmegaCAM camera on ESO’s VLT Survey Telescope in Chile, shows an unusually clean small galaxy. IC 1613 contains very little cosmic dust, allowing astronomers to explore its contents with great clarity.

Many galaxies are chock-full of dust, while others have occasional dark streaks of opaque cosmic soot swirling in amongst their gas and stars. However, the subject of this new image, snapped with the OmegaCAM camera on ESO’s VLT Survey Telescope in Chile, is unusual — the small galaxy, named IC 1613, is a veritable clean freak! IC 1613 contains very little cosmic dust, allowing astronomers to explore its contents with great clarity. This is not just a matter of appearances; the galaxy’s cleanliness is vital to our understanding of the Universe around us.

IC 1613 is a dwarf galaxy in the constellation of Cetus (The Sea Monster). This VST image [1] shows the galaxy’s unconventional beauty, all scattered stars and bright pink gas, in great detail.

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This chart shows the position of the nearby, but very faint, galaxy IC 1613 in the constellation of Cetus (The Sea Monster). Most of the stars visible to the naked eye on a clear and dark night are shown. The galaxy itself has a very low surface brightness and is very hard to spot visually. Credit: ESO/IAU and Sky & Telescope
German astronomer Max Wolf discovered IC 1613’s faint glow in 1906. In 1928, his compatriot Walter Baade used the more powerful 2.5-metre telescope at the Mount Wilson Observatory in California to successfully make out its individual stars. From these observations, astronomers figured out that the galaxy must be quite close to the Milky Way, as it is only possible to resolve single pinprick-like stars in the very nearest galaxies to us.

Astronomers have since confirmed that IC 1613 is indeed a member of the Local Group, a collection of more than 50 galaxies that includes our home galaxy, the Milky Way. IC 1613 itself lies just over 2.3 million light-years away from us. It is relatively well-studied due to its proximity; astronomers have found it to be an irregular dwarf that lacks many of the features, such as a starry disc, found in some other diminutive galaxies.

This sequence starts with a broad view of the rather faint constellation of Cetus (The Sea Monster). As we zoom, we close in on a faint, but nearby galaxy, IC 1613. The final detailed image, captured with the OmegaCAM camera on ESO’s VLT Survey Telescope in Chile, shows an unusually clean small galaxy. IC 1613 contains very little cosmic dust, allowing astronomers to explore its contents with great clarity. Credit: ESO/A. Fujii/Digitised Sky Survey 2. Music: Johan B. Monell (www.johanmonell.com)

However, what IC 1613 lacks in form, it makes up for in tidiness. We know IC 1613’s distance to a remarkably high precision, partly due to the unusually low levels of dust lying both within the galaxy and along the line of sight from the Milky Way — something that enables much clearer observations [2].

The second reason we know the distance to IC 1613 so precisely is that the galaxy hosts a number of notable stars of two types: Cepheid variables and RR Lyrae variables [3]. Both types of star rhythmically pulsate, growing characteristically bigger and brighter at fixed intervals (eso1311).

As we know from our daily lives on Earth, shining objects such as light bulbs or candle flames appear dimmer the further they are away from us. Astronomers can use this simple piece of logic to figure out exactly how far away things are in the Universe— so long as they know how bright they really are, referred to as their intrinsic brightness.

This wide-field view shows the sky around the dwarf galaxy IC 1613 in the constellation of Cetus (The Sea Monster). This picture was created from images forming part of the Digitized Sky Survey 2. The galaxy appears at the centre of the picture as an irregularly shaped clump of faint stars.
This wide-field view shows the sky around the dwarf galaxy IC 1613 in the constellation of Cetus (The Sea Monster). This picture was created from images forming part of the Digitized Sky Survey 2. The galaxy appears at the centre of the picture as an irregularly shaped clump of faint stars.

Cepheid and RR Lyrae variables have the special property that their period of brightening and dimming is linked directly to their intrinsic brightness. So, by measuring how quickly they fluctuate astronomers can work out their intrinsic brightness. They can then compare these values to their apparent measured brightness and work out how far away they must be to appear as dim as they do.

Stars of known intrinsic brightness can act like standard candles, as astronomers say, much like how a candle with a specific brightness would act as a good gauge of distance intervals based on the observed brightness of its flame’s flicker.

Using standard candles — such as the variable stars within IC 1613 and the less-common Type Ia supernova explosions, which can seen across far greater cosmic distances — astronomers have pieced together a cosmic distance ladder, reaching deeper and deeper into space.

Decades ago, IC 1613 helped astronomers work out how to utilise variable stars to chart the Universe’s grand expanse. Not bad for a little, shapeless galaxy.

This video sequence takes a close look at a new image, captured with the OmegaCAM camera on ESO’s VLT Survey Telescope in Chile, showing an unusually clean small galaxy. IC 1613 contains very little cosmic dust, allowing astronomers to explore its contents with great clarity. Credit: ESO. Music: Johan B. Monell (www.johanmonell.com)

Notes

[1] OmegaCAM is a 32-CCD, 256-million-pixel camera mounted on the 2.6-metre VLT Survey Telescope at Paranal Observatory in Chile. Click here to view more images taken by OmegaCAM.

[2] Cosmic dust is made of various heavier elements, such as carbon and iron, as well as larger, grainier molecules. Not only does dust block out light, making dust-shrouded objects harder to see, it also preferentially scatters bluer light. As a result, cosmic dust makes objects appear redder when seen through our telescopes than they are in reality. Astronomers can factor out this reddening when studying objects. Still, the less reddening, the more precise an observation is likely to be.

[3] Other than the two Magellanic Clouds, IC 1613 is the only irregular dwarf galaxy in the Local Group in which RR Lyrae type variable stars have been identified.

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The Space Show this week – Jan.25.16

The guests and topics of discussion on The Space Show this week:

1. Monday, January 25, 2016: 2-3:30 PM PST (5-6:30 PM EST; 4-5:30 PM CST): This is an Indiegogo Co-Host Perk Show featuring TOM MAROTTA with his two guests, CHARLES MILLER and JOSHUA JENKINS. Their topic is March Storm 2016.

2. Tuesday, Jan. 26 , 2016,7-8:30 PM PST (10-11:30 PM EST, 9-10:30 PM CST): We welcome back noted author LORETTA HALL who will discuss her new book, The Complete Space Buff’s Bucket List.

3.SPECIAL TIME: Friday, January 29, 2016, 2016; 2-3:30 PM PST (5-6:30 PM EST; 4-5:30 PM CST) We welcome back FRANK WHITE with STEVE ROITFELD of Steve Roitfeld Productions to discuss The Overview Effect and the film about the subject.

4. Sunday, Jan. 31, 2016: 12-1:30 PM PST (3-4:30 PM EST, 2-3:30 PM CST): OPEN LINES. All space and STEM topics are welcome. First time callers are welcome and wanted.

See also:
* The Space Show on Vimeo – webinar videos
* The Space Show’s Blog – summaries of interviews.
* The Space Show Classroom Blog – tutorial programs

The Space Show is a project of the One Giant Leap Foundation.

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Videos and Images of the East Coast Blizzard of 2016

Here’s a cool time-lapse video of satellite imagery showing the big snow storm over the east coast: NASA’s GEOS-5 provides a satellite view of historic winter storm – Global Modeling and Assimilation Office Research Site

This one is from NOAA:

Here’s a sat image of the blizzard during Saturday morning (Jan.23rd): 2016 Blizzard by Moonlight – NASA

A massive winter storm system pummeled the eastern United States in late January 2016, with two low-pressure systems merging into a potent nor’easter that dropped heavy snow from Virginia to New England. By late afternoon on Jan. 23, snowfall totals were approaching records in several states, and hurricane-force winds were battering the coastlines and leading to serious flooding. The storm was expected to continue through the morning of Jan. 24.

The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite acquired this image of the storm system at 2:15 a.m. EST on Jan. 23. It was composed through the use of the VIIRS “day-night band,” which detects faint light signals such as city lights, moonlight, airglow, and auroras. In the image, the clouds are lit from above by the nearly full Moon and from below by the lights of the heavily populated East Coast. The city lights are blurred in places by cloud cover.

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Here’s an image of the storm as seen from the space station: Scott Kelly on Twitter:

“Massive #snowstorm blanketing #EastCoast clearly visible from @Space_Station! Stay safe! #blizzard2016 #YearInSpace”

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And here is a satellite image showing the East Coast this morning after the clouds have cleared: NASA Sees Dawn and Records Breaking as Major Winter Storm Departs -NASA

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