Space

The Antennae Galaxies, located in the constellation of Corvus (the Crow), are among the closest known merging galaxies. The two galaxies, also known as NGC 4038 and NGC 4039, began interacting a few hundred million years ago, creating one of the most impressive sights in the night sky. They are considered by scientists as the archetypal merging galaxy system and are used as a standard against which to validate theories about galaxy evolution.

Scientists using Hubble’s Advanced Camera for Surveys and Wide Field Planetary Camera 2 to observe individual stars spawned by the colossal cosmic collision in the Antennae Galaxies have reached a surprising conclusion - the Antennae are much closer than previously believed, 45 million light-years instead of the previous best estimate of 65 million light-years.


A team of Dutch and German astronomers have discovered part of the missing matter in the Universe using the European X-ray satellite XMM-Newton. They observed a filament of hot gas connecting two clusters of galaxies. This tenuous hot gas could be part of the missing “baryonic” matter.

The existence of this hot gas (with a temperature of 100 000 - 10 000 000 degrees), known as a warm-hot intergalactic medium, was predicted 10 years ago as a possible source for the missing dark matter. Gas at such high temperature and low density is very difficult to detect and many attempts have failed in past years.

The team observed a pair of clusters of galaxies (Abell 222 and Abell 223) using the European X-ray satellite XMM-Newton. Their observations (see Fig. 1) clearly show a bridge connecting both clusters. The gas they observed there is probably the hottest and densest part of the diffuse gas in the cosmic web, which would be part of the missing “baryonic” dark matter.


A group of researchers writing in Geophysical Research Letters have a new theory about Mercury’s mysterious magnetic field - iron “snow” inside the planet that forms and falls toward the center, much like snowflakes form in Earth’s atmosphere and fall to the ground.

Mercury is the closest planet to the sun and the only other terrestrial planet that possesses a global magnetic field. Discovered in the 1970s by NASA’s Mariner 10 spacecraft, Mercury’s magnetic field is about 100 times weaker than Earth’s. Most models cannot account for such a weak magnetic field.

Made mostly of iron, Mercury’s core is also thought to contain sulfur, which lowers the melting point of iron and plays an important role in producing the planet’s magnetic field.

The Earth's atmosphere is a gigantic prism that disperses sunlight. In the most ideal atmospheric conditions, such as those found regularly above Cerro Paranal, this will lead to the appearance of so-called green and blue flashes at sunset. The phenomenon is so popular on the site that it is now the tradition for the Paranal staff to gather daily on the telescope platform to observe the sunset and its possible green flash before starting their long night of observations.

The green and blue flashes are fleeting events that require an unobstructed view of the setting Sun, and a very stable atmosphere. These conditions are very often met at Paranal, a 2635m high mountain in the Chilean Atacama Desert, where the sky is cloudless more than 300 days a year. Paranal is home of ESO's Very Large Telescope, an ensemble of four 8.2-m telescopes and four 1.8-m Auxiliary Telescopes that together form the world's most advanced optical telescope.


It makes sense that massive black holes lurking in galactic nuclei and weighing millions of Suns can disrupt stars that come too close. Astrophysicists say that the black hole’s gravity pulls harder on the nearest part of the star, an imbalance that pulls the star apart over a period of hours, once it gets inside the so-called "tidal radius."

Two astrophysicists from Paris Observatory say the fate of stars that venture too close to massive black holes could be even more violent than previously believed. Not only are they crushed by the black hole’s huge gravity, but the process can also trigger a nuclear explosion that tears the star apart from within. In addition, shock waves in the pancake star carry a brief and very high peak of temperature outwards, that could give rise to a new type of X-ray or gamma-ray bursts.

Yes, it's galactic flambé.


At the cores of many galaxies, supermassive black holes expel powerful jets of particles at nearly the speed of light. Just how they perform this feat has long been one of the mysteries of astrophysics. The leading theory says the particles are accelerated by tightly-twisted magnetic fields close to the black hole, but confirming that idea required an elusive close-up view of the jet's inner throat. Now, using the unrivaled resolution of the National Radio Astronomy Observatory's Very Long Baseline Array (VLBA), astronomers have watched material winding a corkscrew outward path and behaving exactly as predicted by the theory.


Data from the ESA/NASA spacecraft SOHO shows clearly that powerful starquakes ripple around the Sun in the wake of mighty solar flares that explode above its surface. The observations give solar physicists new insight into a long-running solar mystery and may even provide a way of studying other stars.

The outermost quarter of the Sun’s interior is a constantly churning maelstrom of hot gas. Turbulence in this region causes ripples that criss-cross the solar surface, making it heave up and down in a patchwork pattern of peaks and troughs.


Huge star streams in the outskirts of two nearby spiral galaxies have allowed astronomers to obtain a panoramic overview of ' galactic cannibalism' similar to that involving the Sagittarius dwarf galaxy in the vicinity of the Milky Way.

The detection of these immense stellar fossils confirms the predictions of the cold dark matter model of cosmology, which proposes that present-day grand design spiral galaxies were formed from the merging of less massive stellar systems.

The first of these debris structures surrounds the galaxy NGC 5907, located 40 million light-years from Earth and formed from the destruction of one of its dwarf satellite galaxies at least four billion years ago.


Using NASA, Japanese, and European X-ray satellites, a team of Japanese astronomers has discovered that our galaxy’s central black hole let loose a powerful flare three centuries ago.

The finding helps resolve a long-standing mystery: why is the Milky Way’s black hole so quiescent? The black hole, known as Sagittarius A* (pronounced "A-star"), is a certified monster, containing about 4 million times the mass of our Sun. Yet the energy radiated from its surroundings is billions of times weaker than the radiation emitted from central black holes in other galaxies.

"We have wondered why the Milky Way’s black hole appears to be a slumbering giant," says team leader Tatsuya Inui of Kyoto University in Japan. "But now we realize that the black hole was far more active in the past. Perhaps it’s just resting after a major outburst."


By studying in great detail the 'ringing' of a planet-harbouring star, a team of astronomers using ESO's 3.6-m telescope have shown that it must have drifted away from the metal-rich Hyades cluster. This discovery has implications for theories of star and planet formation, and for the dynamics of our Milky Way.

The yellow-orange star Iota Horologii, located 56 light-years away towards the southern Horologium ("The Clock") constellation, belongs to the so-called "Hyades stream", a large number of stars that move in the same direction.

Previously, astronomers using an ESO telescope had shown that the star harbours a planet, more than 2 times as large as Jupiter and orbiting in 320 days (ESO 12/99).