NGC 6520


NGC 6520 is an open star cluster located about 5,500 light years away towards the constellation Sagittarius. It is about 10 light years across. The bright blue stars are only a few million years old, much younger than our Sun.

Blocking the light of NGC 6520 is Barnard 86, an absorption nebula and molecular cloud. It contains is filled with thick dust that obscures the star cluster. Surrounding the cluster and nebula in this image is part of the dense starscape of our own Milky Way.

Image and information from NASA.

Stars of Taurus


Sun and solar corona passing through Taurus constellation, 31st June 2003.

22 images, about 1 per hour.

Most stars are known by more than one name; have included some alternatives in brackets:

Aldebaran (Alpha Tauri, α Tau) is an orange giant 44 times the size of the Sun, 65 light years away.

Sigma Tauri (σ Tau) is a double star; both components are white dwarfs, 155 light years from the Sun.

Rho Tauri (ρ Tau) is a white dwarf with nearly twice the mass of the Sun, 152 light years away.

Theta Tauri (θ Tau) is another double star but the components, an orange giant and a white giant, are 154 and 150 ly away respectively and the 4 light years separation makes it unlikely they are a binary system.

Hyadum I (the First Hyad, Gamma Tauri, γ Tau) is a red giant in the Hyades star cluster, 154 light years from Earth. Hyadum I is 85 times brighter than the Sun.

Hyadum II (the Second Hyad, Eudora, Delta Tauri, δ Tau), also identified with the Hyades, actually three separate star systems, two of which are composed of three stars – astronomy can be confusing.

Ain (Oculus Borealis, Epsilon Tauri, ε Tau) is an orange giant 147 light years from the Sun. Ain is derived from the Arabic for “eye”; Oculus is from the Latin (Borealis means “north”, as in Aurora Borealis).

Omega Tauri (ω Tau) is an orange giant 291 light years from the sun

Image credit: NASA/ESA/GSFC. Animation: AgeOfDestruction.

Alpha Centauri


Alpha Centauri is a triple star system located only 4.3 light years away towards the constellation Centaurus. It is the closest star system to our own, with Proxima Centauri, the dimmest of the three, as the closest star. Alpha Centauri A and B form a binary system, orbiting each other at a distance only slightly more than that between Uranus and our Sun.

Alpha Centauri A, also called Rigil Kentaurus, is the brightest star in the constellation Centaurus and is the same type of star as our Sun. Alpha Centauri B is smaller and less bright than our Sun, but is still similar. The first Earth sized exoplanet orbiting a Sun like star was discovered orbiting Alpha Centauri B, though its orbit is much too small and thus the planet is much too hot for life as we know it to exist there.

Image from ESO, information from NASA, NASA, and ESO.

Eta Carinae Nebula

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“Eta Carinae is a highly luminous hypergiant star. Estimates of its mass range from 100 to 150 times the mass of the Sun, and its luminosity is about four million times that of the Sun.

This object is currently the most massive star that can be studied in great detail, because of its location and size. Several other known stars may be more luminous and more massive, but data on them is far less robust. Stars with more than 80 times the mass of the Sun produce more than a million times as much light as the Sun. They are quite rare—only a few dozen in a galaxy as big as ours—and they flirt with disaster near the Eddington limit, i.e., the outward pressure of their radiation is almost strong enough to counteract gravity. Stars that are more than 120 solar masses exceed the theoretical Eddington limit, and their gravity is barely strong enough to hold in its radiation and gas, resulting in a possible supernova or hypernova in the near future.

Eta Carinae’s effects on the nebula can be seen directly. The dark globules in the above image and some other less visible objects have tails pointing directly away from the massive star. The entire nebula would have looked very different before the Great Eruption in the 1840s surrounded Eta Carinae with dust, drastically reducing the amount of ultraviolet light it put into the nebula.”

Credit: ESO/Digitized Sky Survey 2.
Acknowledgment: Davide De Martin.

Half of Earth’s water formed before the sun was born

Good news for hunters of extraterrestrial life: Water may be more widespread in planetary systems than previously thought. A team of researchers studying the origin of the water in our solar system has concluded that up to half of it formed before the sun itself was born—that is, in the cloud of dust and gas that was the progenitor of our solar system. If water can form in abundance in such clouds, then it may be found everywhere.

Our solar system is awash with water. Apart from Earth, water is found on the moon, Mars, Mercury, comets, and the icy moons of the giant planets. But where did it come from? Water is known to form in the clouds of gas and dust of the interstellar medium (ISM) from which planetary systems coalesce, but is it destroyed when the newly formed sun starts pumping out heat and light, only to be formed again later? Or does that primordial water survive star formation and remain around us today?

To answer that question, a team led by astronomer L. Ilsedore Cleeves of the University of Michigan, Ann Arbor, focused on deuterium, a heavy form of hydrogen that was created in the big bang along with normal hydrogen. There are about 26 deuterium atoms for every million hydrogen atoms across the universe, but it is six times as prevalent in the water on Earth and in other solar system bodies. Scientists conclude that when the water formed, the reaction creating deuterium-rich “heavy water” was slightly faster than the one creating normal water, so the proportion of deuterium in water increased.

But that enrichment of deuterium happens only under certain conditions: It has to be very cold (only a few tens of degrees above absolute zero), plus you need oxygen and some sort of ionizing radiation to get the reaction going. All of those things are available in the ISM. The ionizing radiation there is cosmic rays, particles from distant sources that zip through space at high speed. And astronomers have observed water in the ISM that is highly enriched in deuterium, so that could be source of the solar system’s water.

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