NGC 3314: When Galaxies Overlap

Credit: W. Keel and R. White, (U. Alabama, Tuscaloosa), Hubble Heritage Team (STScI/ AURA), NASA

Explanation: Can this be a spiral galaxy? In fact, NGC 3314 consists of two large spiral galaxies which just happen to almost exactly line-up. The foreground spiral is viewed nearly face-on, its pinwheel shape defined by young bright star clusters. But against the glow of the background galaxy, dark swirling lanes of interstellar dust are also seen to echo the face-on spiral’s structure. The dust lanes are surprisingly pervasive, and this remarkable pair of overlapping galaxies is one of a small number of systems in which absorption of visible light can be used to directly explore the distribution of dust in distant spirals. NGC 3314 is about 140 million light-years away in the southern constellation of Hydra. Just released, this color composite was constructed from Hubble Space Telescope images made in 1999 and 2000.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

A Panorama of Oddities in Orion A

Credit: T. A. Rector, B. Wolpa, G. Jacoby, AURA, NOAO, NSF

Explanation: New stars, fast jets, and shocked gas clouds all occupy Orion A, a giant molecular cloud just south of the Orion Nebula. The bright object visible below and slightly left of center of this recently released picture is the reflection nebula NGC 1999. Wind from NGC 1999’s central star, V380 Orionis, appears to have created the surrounding billows of red and brown gas. Several bright young stars illuminate reflecting dust at the top right of the image. Jets shoot from dozens of young stars creating glowing compressed shocked waves known Herbig-Haro objects. One such shock is the unusual Waterfall, the bright streak on the upper right, which is a source of unusual radio waves. The cone-shaped shock to the Waterfall’s lower right may result from a jet emitted HH1 and HH2, located 10 light-years away below NGC 1999. The unusual and energetic oddities that occur and interact in star forming regions are often as complex as they are beautiful.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

Supernova 1994D and the Unexpected Universe

Credit: High-Z Supernova Search Team, HST, NASA

Explanation: Far away, long ago, a star exploded. Supernova 1994D, visible as the bright spot on the lower left, occurred in the outskirts of disk galaxy NGC 4526. Supernova 1994D was not of interest for how different it was, but rather for how similar it was to other supernovae. In fact, the light emitted during the weeks after its explosion caused it to be given the familiar designation of a Type Ia supernova. If allType 1a supernovae have the same intrinsic brightness, then the dimmer a supernova appears, the farther away it must be. By calibrating a precise brightness-distance relation, astronomers are able to estimate not only the expansion rate of the universe (parameterized by the Hubble Constant), but also the geometry of the universe we live in (parameterized by Omega and Lambda). The large number and great distances to supernovae measured over the past few years have been interpreted as indicating that we live in a previously unexpected universe.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

NGC 1999: Reflection Nebula in Orion

Credit: Hubble Heritage Team (STScI) and NASA

Explanation: A dusty bright nebula contrasts dramatically with a dusty dark nebula in this Hubble Space Telescope image recorded shortly after December’s orbital servicing mission. The nebula, cataloged asNGC 1999, is a reflection nebula, which shines by reflecting light from a nearby star. Unlike emission nebulae, whose reddish glow comes from excited atoms of gas, reflection nebulae have a bluish cast as their interstellar dust grains preferentially reflect blue starlight. While perhaps the most famous reflection nebulae surround the bright young stars of the Pleiades star cluster, NGC 1999’s stellar illumination is provided by the embedded variable star V380 Orionis, seen here just left of center. Extending right of center, the ominous dark nebula is actually a condensation of cold molecular gas and dust so thick and dense that it blocks light. From our perspective it lies in front of the bright nebula, silhouetted against the ghostly nebular glow. New stars will likely form within the dark cloud, called a Bok globule, as self-gravity continues to compress its dense gas and dust. Reflection nebula NGC 1999 lies about 1500 light-years away in the constellation Orion, just south of Orion’s well known emission nebula, M42.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

Galaxy Wars: M81 Versus M82

Credit & Copyright: Robert Gendler

Explanation: In the left corner, wearing a red nucleus surrounded by blue spiral arms, is M81. In the right corner, sporting light stars and dark dust lanes, is M82. These two mammoth galaxies have been locked in gravitational combat for the past billion years. The gravity from each galaxy dramatically affects the other during each hundred million-year pass. Last go-round, M82’s gravity likely raised circulating density waves rippling around M81 resulting in the richness of M81’s spiral arms. M81, though, left M82 a messy pulp of exploded stars and colliding gas so violent it emits bright X-rays. In both galaxies, colliding gas has created a recent abundance of bright new stars. In a few billion years only one galaxy will remain.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

Colorful Clouds Of Carina

Credit: Hubble Heritage Team (AURA/ STScI), NASA

Explanation: Tumultuous clouds of the Carina Nebula, 8000 light-years away, glow in planet Earth’s southern sky. Striking and detailed, this close-up of a portion of the famous nebula is a combination of exposures through six different filters taken with the Hubble Space Telescope’s Wide Field Planetary Camera 2 in April of 1999. Dramatic dark dust knots and complex features revealed are sculpted by the winds and radiation of Carina’s massive and energetic stars. But how were this picture’s colors generated? Astronomical images produced from Hubble Space Telescope data can be composed of exposures made using relatively narrow filters which don’t match the color responses of the human eye. Some of the filters even transmit wavelengths of light outside the visible spectrum. Exposures made with different narrow filters, as in this case, are translated to a visible color where shorter wavelengths are assigned bluer and longer wavelengths assigned redder colors. This color scheme represents a “chromatically ordered” way of presenting the data rather than a natural color image.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

X For Andromeda

Credit: S. Murray, M. Garcia, et al., (CfA) SAO, CXO, NASA

Explanation: A big beautiful spiral galaxy 2 million light-years away, Andromeda (M31) has long been touted as an analog to the Milky Way, a distant mirror of our own galaxy. The popular 1960s British sci-fi series, A For Andromeda, even postulated that it was home to another technological civilization that communicated with us. Using the newly unleashed observing power of the orbiting Chandra X-ray telescope, astronomers have now imaged the center of our near-twin island universe, finding evidence for an object so bizarre it would have impressed many 60s science fiction writers (and readers). Like the Milky Way, Andromeda’s galactic center appears to harbor an X-ray source characteristic of a black hole of a million or more solar masses. Seen above, the false-color X-ray picture shows a number of X-ray sources, likely X-ray binary stars, within Andromeda’s central region as yellowish dots. The blue source located right at the galaxy’s center is coincident with the position of the suspected massive black hole. While the X-rays are produced as material falls into the black hole and heats up, estimates from the X-ray data show Andromeda’s central source to be surprisingly cool – only a million degrees or so compared to the tens of millions of degrees indicated for Andromeda’s X-ray binaries.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

A Skygazer’s Full Moon

Credit & Copyright: Robert Gendler

Explanation: This dramatically sharp picture of the full moon was recorded on 22 December, 1999 by astroimager Rob Gendler. Big, beautiful, bright, and evocative, it was the last full moon of the Y1.9Ks, pleasing and inspiring even casual skygazers. December’s moon was special for another reason, as the full phase occurred on the day of the winter solstice and within hours of lunar perigee. The first full moon of the year 2000 will bring a special treat as well, presenting denizens of planet Earth with a total lunar eclipse. On Thursday evening, January 20, the moon will encounter the dark edge of Earth’s shadow at 10:01 PM Eastern Time with the total eclipse phase beginning at 11:05 PM and lasting for 77 minutes. This lunar eclipse will be visible from North and South America and Western Europe (total phase begins at 4:05 AM GMT January 21).

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)