MyCn18: An Hourglass Nebula

Credit: R. Sahai and J. Trauger (JPL), WFPC2, HST NASA

Explanation: The sands of time are running out for the central star of this hourglass-shaped planetary nebula. With its nuclear fuel exhausted, this brief, spectacular, closing phase of a Sun-like star’s life occurs as its outer layers are ejected – its core becoming a cooling, fading White Dwarf. Astronomers have recently used the Hubble Space Telescope (HST) to make a series of images of planetary nebulae, including the one above. Here, delicate rings of colorful glowing gas (nitrogen-red, hydrogen-green, and oxygen-blue) outline the tenuous walls of the “hourglass”. The unprecedented sharpness of the HST images has revealed surprising details of thenebula ejection process and may help resolve the outstanding mystery of the variety of complex shapes and symmetries of planetary nebulae.

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

Antares and Rho Ophiuchi

Credit & Copyright: D. Malin (AAO), AATB, ROE, UKS Telescope

Explanation: Why is the sky near Antares and Rho Ophiuchi so colorful? The colors result from a mixture of objects and processes. Fine dust illuminated from the front by starlight produces blue reflection nebulae. Gaseous clouds whose atoms are excited by ultraviolet starlight produce reddish emission nebulae. Backlit dust clouds block starlight and so appear dark. Antares, a red supergiant and one of the brighter stars in the night sky, lights up the yellow-red clouds on the upper left. Rho Ophiuchi lies at the center of the blue nebula on the right. The distant globular cluster M4 is visible just below Antares, and to the left of the red cloud engulfingSigma Scorpii. These star clouds are even more colorful than humans can see, emitting light across the electromagnetic spectrum.

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

The North America Nebula

Credit & Copyright: Jason Ware

Explanation: Here’s a familiar shape in an unfamiliar location! This emission nebula is famous partly because it resembles Earth’s continent of North America. To the right of the North America Nebula, cataloged as NGC 7000, is a less luminous Pelican Nebula. The two emission nebula measure about 50 light-years across, are located about 1500 light-years away, and are separated by a dark absorption cloud. The nebulae can be seen with binoculars from a dark location. Look for a small nebular patch north-east of bright star Deneb in the constellation of Cygnus. It is still unknown which star or stars ionize the red-glowing hydrogen gas.

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

Filaments In The Cygnus Loop

Credit: William P. Blair and Ravi Sankrit (Johns Hopkins University), NASA

Explanation: Subtle and delicate in appearance, these are filaments of shocked interstellar gas — part of the expanding blast wave from a violent stellar explosion. Recorded in November 1997 with the Wide Field and Planetary Camera 2 onboard the Hubble Space Telescope, the picture is a closeup of a supernova remnant known as the Cygnus Loop. The nearly edge-on view shows a small portion of the immense shock front moving toward the top of the frame at about 170 kilometers per second while glowing in light emitted by atoms of excited Hydrogen gas. Not just another pretty picture, this particular image has provided some dramatic scientific results. In 1999, researchers used it to substantially revise downward widely accepted estimates of distance and age for this classic supernova remnant. Now determined to lie only 1,440 light-years away, the Cygnus Loop is thought to have been expanding for 5 – 10 thousand years.

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

Eagle EGGs in M16

Credit: J. Hester & P. Scowen (ASU), HST, NASA

Explanation: Star forming regions known as “EGGs” are uncovered at the end of this giant pillar of gas and dust in the Eagle Nebula (M16). EGGs, short for evaporating gaseous globules, are dense regions of mostly molecular hydrogen gas that fragment and gravitationally collapse to form stars. Light from the hottest and brightest of these new stars heats the end of the pillar and causes further evaporation of gas – revealing yet more EGGs and more young stars. This picture was taken by the Wide Field and Planetary Camera on board the Hubble Space Telescope.

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

 

M20: The Trifid Nebula

Credit & Copyright: Todd Boroson, AURA, NOAO, NSF

Explanation: Unspeakable beauty and unimaginable bedlam can be found together in the Trifid Nebula. Also known as M20, this photogenic nebula is visible with good binoculars towards the constellation of Sagittarius. The energetic processes of star formation create not only the colors but the chaos. The red-glowing gas results from high-energy starlight striking interstellar hydrogen gas. The dark dust filaments that lace M20 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions. Which bright young stars light up the blue reflection nebula is still being investigated. The light from M20 we see today left perhaps 3000 years ago, although the exact distance remains unknown. Light takes about 50 years to cross M20.

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)

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)

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)

The Eskimo Nebula from the Newly Fixed Hubble

Credit: Andrew Fruchter (STScI) et al., WFPC2, HST, NASA

Explanation: In 1787, astronomer William Herschel discovered the Eskimo Nebula. From the ground, NGC 2392 resembles a person’s head surrounded by a parka hood. In 2000, just after being fixed, theHubble Space Telescope imaged the Eskimo Nebula. From space, the nebula displays gas clouds so complex they are not fully understood. The Eskimo Nebula is clearly a planetary nebula, and the gas seen above composed the outer layers of a Sun-like star only 10,000 years ago. The inner filaments visible above are being ejected by strong wind of particles from the central star. The outer disk contains unusual light-year long orange filaments. The Eskimo Nebula lies about 5000 light-years away and is visible with a small telescope in the constellation of Gemini.

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