A Star and a Nebula

A cosmic coupleThat’s the star Hen 2-427 (aka WR 124) at the center of this picture. It’s surrounded by the nebula M1-67. They’re found in the constellation of Sagittarius about 15,000 light-years away. The star shines brightly at the very center of these hot clumps of surrounding gas that it’s ejecting into space at over 150,000 km per hour.

Hen 2-427 is a Wolf–Rayet star. Named after the astronomers Charles Wolf and Georges Rayet, Wolf–Rayet stars are super-hot and characterized by a fierce ejection of mass. In this case, that results in the nebula M1-67 which is estimated to be less than 10,000 years old, a newbie in astronomical terms,

Image Credit: ESA

NGC 2022

NGC 2022 is a planetary nebula in the constellation Orion. In early telescopes (and in today’s medium-sized amateur telescopes) such nebulae look like small grayish patches of light. Since they don’t look like stars, but a bit like the gas giant planets, early astronomers tagged them as “planetary nebula,” and the name has stuck.

When stars like the Sun grow old, they expand into red giants. They then begin to lose their outer layers into space, forming a shell of gas. As the evolving star’s core shrinks and grows hotter, it emits ultraviolet light that causes the expelled gases to glow.

Image Credit: NASA / ESA

Messier 69

This is an image of the core fo the globular star cluster Messier 69. It is made up of visible light and infrared data taken by the Hubble Space Telescope. The cluster was discovered by Charles Messier in 1780. It’s located 29,700 light-years from Earth in the constellation Sagittarius. It’s too dim to be seen with the naked eye, but it can be viewed with a pair of binoculars, especially during August.

The stars in M69 have over ten times more iron than stars in other globular clusters of the same age. Iron is the heaviest element created by fusion in a star unless it explodes as a supernova.

Image Credit: NASA / ESA

A Colossal Interaction

An interacting colossusThis picture shows a galaxy known as NGC 6872 in the constellation of Pavo (The Peacock). Its unusual shape is caused by its interactions with the smaller galaxy called IC 4970 that can be seen just above it. The pair are roughly 300 million light-years away from Earth.

NGC 6872 measures over 500,000 light-years across. It’s the second largest spiral galaxy discovered thus far. Our own galaxy, the Milky Way, measures around 100,000 light-years across.

The upper left spiral arm of NGC 6872 appears distorted and is filled with star-forming regions which appear blue on this Hubble image. That may have been be caused by IC 4970 recently (only about 130 million years ago) passing through this spiral arm. Astronomers have noted that NGC 6872 seems to be relatively sparse in terms of free hydrogen, which is the basis material for new stars. It is probable that if it weren’t for its interactions with IC 4970, NGC 6872 might not have been able to produce these new bursts of star formation.

Image Credit: NASA / ESA

A Starbursting Galaxy

This is the dwarf galaxy known as NGC 1140. It lies 60 million light-years away in the constellation of Eridanus. It has an irregular form, much like the Large Magellanic Cloud, a small galaxy that orbits the Milky Way. This small galaxy is undergoing a starburst. Despite being only about one-tenth the size of the Milky Way, it is creating stars at about the same rate—the equivalent of one star the size of our sun being created per year. The galaxy is full of bright, blue-white, young stars.

Galaxies like NGC 1140 are of particular interest to astronomers because their composition makes them similar to the intensely star-forming galaxies in the early Universe, and those early Universe galaxies were the building blocks of present-day large galaxies like our Milky Way. Because they are so far away, the early Universe galaxies are harder to study, so these closer starbursting galaxies are a good substitute for studyingt galaxy evolution.

Its vigorous star formation eventually will have a very destructive effect on this small dwarf galaxy. When the larger stars in the galaxy die and explode as supernovae, the gas blown into space may escape the gravitational pull of the galaxy. The ejection of gas from the galaxy throws away one of the building blocks for future star formation. Thus, NGC 1140’s starburst cannot last for long.

Image Credit: ESA