Category: Letters

Merging Y

NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

Galaxy interactions are always impressive. ESO 593-8 looks like the letter “Y,” swooping eagle or a feather. Explore the NASA Hubble Space Telescope image of these merging galaxies. Do you see any patterns? What stories can you tell?

The two spiral galaxies will probably merge to form a single galaxy in the future. Look for dark lanes of dust and bright blue star clusters at the outer fringes of the galaxies. When galaxies interact, gas and dust are pushed together. The gas and dust can collapse under its own gravity and new stars are formed. However, exist­ing stars them­selves are not really dis­rupted by the merger. After sev­eral mil­lion years, the black holes at the center of these galaxies will merge and the stars will set­tle into new orbits around a new galac­tic cen­ter.

A number of faint background galaxies can be found throughout the image. The bright stars are foreground stars in our own Milky Way Galaxy.

ESO 593-8 lies about 650 million light-years from Earth toward the constellation Sagittarius, the Archer. A light-year is the distance light travels in a year; about 6 trillion miles. When light left this galaxy pair, many geologists believe Earth’s surface was almost entirely covered by ice in what’s known as Snowball Earth or Marinoan Glaciation. But the planet was on the verge of a sudden explosion in the diversity in life. During the later Proterozoic, bacteria and green algae were common in the seas of Earth. Soft-bodied worms swam in these seas. Animals had not yet ventured onto land.

Xs, Boomerangs and Butterflies

Credit: NASA & ESA

The wings of gas and dust of the Boomerang Nebula blossom into the letter X. NASA’s Hubble Space Telescope took this image of twin reflecting clouds of gas and dust being ejected from this star. Astronomers call these bi-polar nebulae, butterfly nebulae or bow-tie nebulae. Scientists aren’t sure why the material from the star is being ejected in this way. Perhaps denser material across the star’s middle is forcing the star to eject gas and dust at the star’s poles. Or, maybe magnetic fields are funneling material toward the poles.

Explore the nebula. Travel from the central star along the wings of the nebula. Each wing of this nebula is more than a light-year long. Altogether this whole nebula would reach from the Sun to halfway to our nearest stellar neighbor, Alpha Centauri.

The Boomerang Nebula lies about 5,000 light years away toward the southern constellation of Centaurus.

Swirling W

Credit: NASA and the Hubble Heritage Team (STScI)

Looping arcs of stars and dust create a cosmic letter “W” caught in the middle of this galactic encounter.

Explore the NASA Hubble Space Telescope image of spiral galaxies NGC 2207, on the left, and IC 2163, on the right. The strong gravitational tug of NGC 2207 has already distorted the shape of the smaller galaxy. The larger galaxy looks like a huge saw blade whirling into the smaller galaxy. Or is it the other way around? Gravity flings stars and gas out of IC 2163 in long streamers a 100,000 light-years long. Look for the dark lane of dust from the larger NGC 2207 as it cuts above the smaller galaxy. Looking through this dust makes the light from IC 2163 redder in color. Follow the outer arms of NGC 2207 and explore the huge star clouds. These areas glow blue with new star birth. Several pockets of new stars can be seen in the outer spiral arms of these galaxies.

From this embrace neither galaxy will escape. The galaxies will swirl around each other, coming closer and closer, before merging into a single large galaxy in a billion years. Many of the galaxies we see in the night sky, including our own Milky Way, have gone through cosmic collisions to become larger galaxies.

This pair of spiral galaxies is found about 114 million light-years from Earth toward the constellation of Canis Major, the Large Dog.

Disturbed “V”

Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

Galaxies collide to form this highly disturbed “V” in this NASA Hubble Space Telescope image of interacting galaxy IC 883.

What other shapes do you see in the star clouds that make up this galaxy? Explore the complex central region. Two tidal tails shoot off at right angles to each other; the remnants of two gas-rich galaxies. The gas and dust from the tails gets stretched and spun out during the merger. The collision seems to have triggered intense star formation within the chaotic and stretched core. Look for the bright blue star clusters amid the dark During galactic mergers, gas and dust get stretched and pulled. Some of this material clumps together and begins to smash together under gravity. If enough material comes together, a star can form. Zoom in on the dozens of elliptical and spiral galaxies in the distant background of IC 883.

IC 883, is located about 300 million light-years from Earth toward the constellation Canes Venatici, the Hunting Dogs of Bootes.

Gravitational “U”

Credit: NASA, ESA, R. Gavazzi and T. Treu (University of California, Santa Barbara), and the SLACS team

The great gravity of an elliptical galaxy warps the light of two other galaxies to form a “U” in this image of a gravitational lens by NASA’s Hubble Space Telescope.

Explore this image of the deep universe. The massive elliptical galaxy about 3 billion light-years from Earth toward the constellation Leo, the Lion, is almost perfectly lined up with two other distant galaxies. The whole group is called gravitational lens system SDSSJ0946+1006. The gravity from the bright galaxy in the center bends the light of the distant objects like a magnifying glass bends light. What we see is a distorted arc of light that is shifted from its original position.

Astronomers call these Einstein rings, or arcs. Albert Einstein predicts in his theory of general relativity that gravity warps space-time and can bend light. This theory has been confirmed many times since, most famously during a solar eclipse in 1919 when astronomers observed the bent light of stars close to the sun, making them to appear out of position.

Another example of a distant gravitational lens. Credit: European Space Agency, NASA, Keren Sharon (Tel-Aviv University) and Eran Ofek (CalTech)


The ancient peoples saw pictures in the sky. From those patterns in the heavens, ancient storytellers created legends about heroes, maidens, dragons, bears, centaurs, dogs and mythical creatures...
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