Category: Astronomy

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A new glimpse inside the heart of Orion has confirmed the separation between the binary star system that orbit each other so closely, astronomers once believed they could be a single star.

The research team, led by Stefan Kraus and Gerd Weigelt from the Max-Planck-Institute for Radio Astronomy (MPIfR) in Bonn, Germany, used ESO’s Very Large telescope Interferometer (VLTI) to obtain the sharpest ever image of the young double star Theta 1 Ori C in the Orion Trapezium Cluster.

The binary stars represent the most massive star in the nearest high-mass star-forming region to Earth. 

Theta 1 Ori C is the dominant and most luminous star in the Orion star nursery. Located at a distance of only about 1,300 light years, it provides a unique laboratory to study the formation process of high-mass stars in detail. The intense radiation of Theta 1 Ori C is ionizing the whole Orion nebula. With its strong wind, the star pair also shapes the famous Orion proplyds, young stars still surrounded by their protoplanetary dust disks.

Although Theta 1 Ori C appeared to be a single star, both with conventional telescopes and the Hubble Space Telescope, the team discovered the existence of a close companion.

“VLTI interferometry with the AMBER instrument allowed us, for the first time, to obtain an image of this system with the spectacular angular resolution of only 2 milliarcseconds”, says Stefan Kraus. “This corresponds to the resolving power of a space telescope with a mirror diameter of 130 meters.”

The new image clearly separates the two young, massive stars of this system. The observations have a spatial resolution of about 2 milliarcseconds, corresponding to the apparent size of a car on the surface of the Moon. 

The VLTI image reveals that in March 2008 the angular distance between the two stars was only about 20 milliarcseconds. Additional position measurements of the binary system have been obtained over the last 12 years using the technique of bispectrum speckle interferometry with 3.6- to 6-meter-class telescopes, allowing high-angular resolution observations even at visual wavelengths down to 440 nm.

The collection of measurements shows that the two massive stars are on a very eccentric orbit with a period of 11 years. Using Kepler’s third law, the masses of the two stars were derived to be 38 and 9 solar masses. Furthermore, the measurements allow a trigonometric determination of the distance to Theta 1 Ori C and, thus, to the very center of the Orion star-forming region.

The resulting distance of 1,350 light-years is in excellent agreement with the work of another research group led by Karl Menten, also from MPIfR, who measured trigonometric parallaxes of the nonthermal radio emission of Orion Nebula stars using the Very Long Baseline Array. These results are important for studies of the Orion region as well as the improvement of theoretical models of high-mass star formation.

The researchers say the results highlight new possibilities of high-resolution stellar imaging achievable with infrared interferometry. The technique allows astronomers to combine the light from several telescopes, forming a huge virtual telescope with a resolving power corresponding to that of a single telescope with 200 meters diameter. 

“Our observations demonstrate the fascinating new imaging capabilities of the VLTI,” said Gerd Weigelt. “This infrared interferometry technique will certainly lead to many fundamental new discoveries.”

LEAD IMAGE CAPTION: VLTI/AMBER image of Theta 1 Ori C in the Orion Trapezium Cluster, plus position measurements of the binary system obtained over the last 12 years. Credit: Max Planck Institute/VLTI/AMBER

Sources: Max Planck Institute press release (emailed through Eurekalert), and the original paper.

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As you probably know, lava is the molten rock that comes out of volcanoes during eruptions. But what is it? What is lava, and how does it get so hot?

You’re standing on the Earth’s crust right now. But beneath your feet, the interior of the Earth gets must hotter. About 30 km beneath the Earth’s crust is the mantle; a vast region of hot rock that can be thousands of degrees. Although the mantle is mostly solid, it can form pockets of liquid rock called magma. This lava is much less dense than the surrounding rock, and so it “floats” up to the surface of the Earth through cracks and weaknesses in the Earth’s crust.

When it finally reaches the Earth’s surface and escapes, geologists call this hot rock magma. It’s still the same stuff, it’s just at the surface of the Earth now. Different kinds of lava will flow at different speeds when they erupt from a volcano. The least thick can flow in great rivers of molten rock for many kilometers. The thicker lava doesn’t flow very far at all, piling up around the volcanic vent, and creating the familiar cone shaped volcano. The thickest stuff doesn’t really flow at all, it just plugs up the volcano’s plumbing, and can lead to powerful explosions.

Lava can range in temperature from about 750 degrees C to more than 1100 C. The temperature of the lava actually depends on the composition of the minerals in it. Some contain large amounts of aluminum, potassium and calcium, while others have iron and magnesium.

We have written many articles about volcanoes for Universe Today. Here’s an article about how a volcano triggered a lightning storm, and here’s an article about the temperature of lava.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

There are several different types of volcanoes: steep stratovolcanoes, wide shield volcanoes, and mounded lava domes. The shape of a volcano actually depends on the types of lava that it’s made up of. And so, there are several different types of lava.

The type of lava coming out of a volcano depends on its mineral content. Some lava is very thin, and can flow out of a volcano in great rivers that go for dozens of kilometers. Other lava is very thick, and only flows for a short distance before cooling and hardening. And some lava is so thick that it barely “flows” at all, and can plug up the plumbing of a volcano.

The main types of lava have been given Hawaiian names, because of the volcanic nature of the Hawaiian islands. You can find examples of different kinds of lava flows on the island.

A’a
Pronounced “ah-ah”, this is a basaltic lava that doesn’t flow very quickly. It looks like a slowly moving mass of hot jello, with cooler, rough surface. Once it hardens, the sharp spiny surface of a’a lava is extremely difficult to walk across. These types of lava erupt at temperatures above 1000 to 1100 degrees C.

Pahoehoe
Pronounced “pa-ho-ho”, this type of lava is much thinner and less viscous than a’a. It can flow down the slopes of a volcano in vast rivers. The surface of the lava congeals into a thin crust that looks very smooth. Pahoehoe lava can also form lava tubes, where the rock hardens around a fast-moving liquid core. When that core flows out of the tube, a long tunnel remains. Pahoehoe erupts at temperatures of 1100 to 1200 C.

Pillow Lava
Pillow lava is typically found erupting from underwater volcano vents. As soon as the lava contacts the water, it’s cooled down and forms a hardened shell. As more lava issues from the vent, the shell of lava cracks and more “pillows” come out of these cracks.

We have written many articles about volcanoes for Universe Today. Here’s an article about the temperature of lava.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

The temperature of lava when it is first ejected from a volcanic vent can vary between 700 and 1,200 degrees C (1,300 to 2,200 F).

As you probably know, lava is molten rock that comes out of a volcano during an eruption. Although the Earth’s mantle is solid, it’s so hot that puddles of molten rock can form between the mantle and the Earth’s crust. This lava is less dense than the surrounding rocks, and so it makes its way to the surface through cracks and faults in the Earth’s crust. Eventually, it erupts to the surface.

Even though lava is much thicker than water, it can flow great distances across the surface of the Earth before it cools and hardens. Some lava is very thin, and can flow many kilometers, while other lava is thick and doesn’t flow at all; it just piles up around the volcanic vent.

Whether lava is thick or thin doesn’t depend on the temperature of the lava. Instead it’s caused by the minerals in the lava. The coolest lava are felsic lavas, which can erupt at temperatures as low as 650-750 C. Next are the andesitic lavas, which erupt in the range of 750-950 C. Basaltic lavas typically erupt at temperatures above 950 C.

We have written many articles about volcanoes for Universe Today. Here’s an article about the recent eruption of Alaska’s Redoubt volcano, and here’s an article about the biggest volcano on Earth.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

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Stratovolcanoes, or composite volcanoes, are some of the largest, most familiar mountains on Earth. Perhaps you’ve heard of Mount Fuji, Mount Kilimanjaro, or Mount Rainier? These are stratovolcanoes. They’ve got that familiar shape with the gently sloping lower sides and then the sharp cone shape at the top. They make up 60% of the Earth’s individual volcanoes.

They typically have a layered or stratified appearance, with alternating lava flows, mudflows, fallen ash, and other debris. They usually form along the margins of the Earth’s tectonic plates, where one plate is pushing beneath another, or they’re sliding together. This creates weaknesses in the Earth’s crust, where magma from beneath the surface can escape.

Stratovolcanoes will usually have a central caldera, or crater, at the top, but they will also have a network of vents. They can have many lava domes and smaller vents where eruptions can occur; not just from the top. The lava flows out of them is extremely thick, and sometimes it barely flows at all. This lava plugs up the plumbing in stratovolcanoes, allowing them to build up tremendous amounts of pressure.

Of all the volcanoes on Earth, stratovolcanoes are the most dangerous. They can erupt with little warning, releasing enormous amounts of material. And they don’t always erupt nicely from their tops. As we saw with Mount Saint Helens, they can blast out material from the side, creating pyroclastic flows the hurtle down the volcano’s flanks at enormous speeds. Some classic eruptions of stratovolcanoes include the island of Krakatoa, which detonated in 1883, sending ash 80 km into the atmosphere.

We have written many articles about volcanoes for Universe Today. Here’s an article about how a volcano triggered a lightning storm. And here’s an article about the largest volcano in the Solar System.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

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Not all volcanoes are the familiar cone-shaped mountains with lava spewing out of the top. Sometimes you can get a very slow eruption, underneath the ground, where a mound of earth rises up above the surroundings. These are called lava domes.

Lava domes form when you have slow eruption of very thick lava, or multiple eruptions of different kinds of lava. Instead of breaking through to the surface, the material builds up underneath the ground, causing the huge lava dome mound to form. It’s so thick that the lava can’t flow very far at all, it just hardens quickly, extruding new material around the vent. They can grow for months or years, eventually building up to several hundred meters in height. Large composite volcanoes can have hundreds of lava domes across their flanks.

The sides of lava domes are very steep, and can cause rockslides around because of the extrusion of new lava. This can bury the surrounding landscape, and even start forest fires if the rocks are still hot. The surfaces of lava domes are rough and blocky because of the fragmentation of rock shell as the dome grows.

As you can probably guess, this buildup of lava and gas can be dangerous. Although people can avoid the growth of a lava dome, they can be a problem for buildings that can’t be moved. But an even more dangerous problem with lava domes is the fact that they can explode violently, without warning, releasing pyroclastic flows of ash and mud for more than 20 km around the dome itself. In 1902, an eruption from a dome on Mont Pelee in Martinique killed 30,000 people with high-velocity ash flow and poisonous gasses.

We have written many articles about volcanoes for Universe Today. Here’s an article about how a volcano in Chile triggered a lightning storm, and here’s an article about cinder cone volcanoes.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.