Star exploration

A new visualization provides an exceptional virtual trip – complete with a 360-degree view – to the center of our home galaxy, the Milky Way. This project, made using data from NASA’s Chandra X-ray Observatory and other telescopes, allows viewers to control their own exploration of the fascinating environment of volatile giant stars and powerful gravity around the monster black hole that lies in the Galactic center. 

The Earth is located about 26,000 light years, or about 150 trillion miles, from the center of the Galaxy. While humans cannot physically travel there, scientists have been able to study this region by using data from powerful telescopes that can detect light in a variety of forms, including X-ray and infrared light.

This visualization builds on infrared data with the European Southern Observatory’s Very Large Telescope of 30 massive stellar giants called Wolf-Rayet stars that orbit within about 1.5 light years of the center of our Galaxy. Powerful winds of gas streaming from the surface of these stars are carrying some of their outer layers into interstellar space. When the outflowing gas collides with previously ejected detritus from other stars, the collisions produce shock waves, similar to sonic booms, which permeate the area. These shock waves heat the gas to millions of degrees, which causes it to glow in X-rays. Extensive observations with Chandra of the central regions of the Milky Way have provided critical data about the temperature and distribution of this multimillion-degree gas.

Astronomers are interested in better understanding what role these Wolf-Rayet stars play in the cosmic neighborhood at the Milky Way’s center. In particular, they would like to know how the stars interact with the Galactic center’s most dominant resident: the supermassive black hole known as Sagittarius A* (abbreviated Sgr A*). Pre-eminent yet invisible, Sgr A* has the mass equivalent to some four million Suns.

The Galactic Center visualization is a 360-degree movie that immerses a viewer into a simulation of the center of our Galaxy. The viewer is at the location of Sgr A* and is able to see about 20 massive stars (white, twinkling objects) orbiting Sgr A* as they continuously eject stellar winds (black to red to yellow color scale). These winds collide with each other, and then some of this material spirals towards Sgr A*. The movie, which starts 350 years in the past, spans 500 years.

The researchers, led by Christopher Russell of the Pontifical Catholic University of Chile, used the visualization to understand the presence of a previously-detected ring of X-rays that extends about 0.6 light years outward from Sgr A*. The information provided by the visualization and the theoretical modeling led Russell and his colleagues to determine that Sgr A* had a relatively powerful outburst that started within the last few centuries. Moreover, their findings suggest the outburst from the supermassive black hole is still affecting the X-ray emission around Sgr A* even though it ended about one hundred years ago.

The 360-degree video of the Galactic Center is ideally viewed in virtual reality (VR) goggles, such as Samsung Gear VR or Google Cardboard. The video can also be viewed on smartphones using the YouTube app. Moving the phone around pans to show a different portion of the movie, mimicking the effect in the VR goggles. Most browsers on a computer also allow 360-degree videos to be shown on YouTube. To look around, either click and drag the video, or click the direction pad in the corner.

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Credits: NASA

Spring Sky

In the northern sky, you may notice an interesting geometry like a ‘dipper’. These 7 stars geometry is known as the Plough, which is a part of Ursa Major’ (Great Bear). Counting from the end of the handle, the second star could be discovered as a double upon closer inspection. It is hard to tell there is 2 stars unless you have good eyesight. In ancient it was an eyesight test for the soldiers. 

When you connect Dubhe and Merak with an imaginary line, and extend the line due north to about 5 times than distance between these stars, you can locate the north pole star. The pole star appears stationary in the north. It is because that the Earth’s rotating axis is pointing to it. Pole star belongs to the Ursa Minor which also known as Little Dipper.

Another famous constellation in Spring is Leo. From the Plough, if you extend the imaginary line drawing from Megrez to Phad, you could easily locate the brightest star of Leo – Regulus. Leo could be easily recognised by the groups of stars resembling a large crescent or reversed question mark.

If you further extend the arc of the handle of the Plough towards the equator, you would encounter the orange star Arcturus in Bootes, or Herdsman. Bootes shaped like a kite in the sky. In Greek myth, it is said that Bootes has a role to herd the stars around the North Pole eternally. Farther along the arc extending from Plough, below the equator, there is a bright star Spica that lies in Virgo. Virgo is often represented as a “maiden” (as its name indicates). In antiquity, she may have been Isis, the Egyptian protectress of the living and the dead and the principal mother goddess. In fact, stars of Virgo and Bootes are scattered and fainter, which is relatively harder to find.

The three bright stars Regulus, Arcturus and Spica form a prominent Trangle in the sky, and it is known as the “Spring Triangle”.

Summer Sky

Under good weather, it is not difficult to find a faint band across the sky, which is known as the Milky Way. It serves as a good guide to locate constellations, such as Sagittarius (the Archer). It appears in the southern sky and it lies in the brightest part of the Milky Way, which could be noticed for its close bright stars. You may easily recognise Sagittarius by its teapot shape. In Greek myth, it is an archer but it is a half-man, half-beast creature. Its bow is pointing to Scorpius, the adjacent constellation at the west. Scorpius is one of the few constellations whose shape can be imagined from its name. It shaped as a skewed “S” hanging on the southern sky, really like a Scorpion. The curving line of stars forms its tail with its sting raised to strike. Along the body of scorpion, you will get see a reddish-orange bright star, namely Antares. This is the heart of the scorpion. Along the Milky Way, if you sweep up to the north, you will find 3 bright stars, which is known as the “summer Triangle”. One of the bright stars, Deneb, lies in the tail of Cygnus. Cygnus appears like a swan flies with outspread wings along the Milky Way. Because of its shape, it is sometimes also know as the Northern Cross. From old stories, the swan is Orpheus, who was killed by Achilles at the battle of Trop and placed in the stars near his beloved harp (Lyra). Another Star of the “Summer Triangle” is called Vega, which appears blue-white. It is a member of Lyra. Lyra is relatively small constellation in the sky, which like a triangle formed by Vega and 2 fainter stars on the east. The lyre is one of the most ancient of musical instruments. In Greek mythology, the lyre was invented by Hermes and given to Apollo his half-brother, who in turn gave it to his son Orpheus, the musician of the Argonauts. Another bright star, Altair, and it mark the constellation Aquila. Aquila can be recognised by its pure white light and the presence of two fainter stars. During the summer time it is about 45¢X above the horizon as seen from mid-northern latitudes. In Greek myth, it was Zeus’s pet Eagle. It was involved in how people got fire.

Autumn Sky

In autumn, a good starting point is to locate the Cassiopeia first. It shaped like a “W” which could be easily distinguished from the stars at the northeast. You can also find it by extending the line formed by Merak and Dubhe at the Big Dipper, and Polaris. Cassiopeia consists of 5 bright stars, which forming a peculiar W shape or M shape. In Greek Legend, Cassiopeia is the wife of King Cepheus of Ethiopia. 

Not far from Cassiopeia is the renowned ” Great Square of Pegasus” in the authumn sky. Pegasus, which also known as the Flying Horse. The square is the body of the horse, and when it is rising in the east is often liken to a diamond. The horse is orientated upside down if viewed in the north of equator, while appears upright in the south. Pegasus contains one of the best globular clusters (M15) for small telescope, also it is believed there may be a black hole at the center. In Greek myth, Pegasus became Zeus’ packhorse, which carries lightning to where it was needed.

When traced northeast from the “Square”, you could pick out the Andromeda. In Greek myth, Andromeda is a chained or girdled lady. She is seen in the sky with her arms stretched out, and lies with her head at the upper left corner of the “Square”. The most striking feature here is that the largest and nearest spiral galaxy is located in this northern part of the figure, the so-called (M31). It appears as a fuzzy elongated patch of light, which could be observed through binoculars.

When you extend the line from Tsih to Ruchban in Cassiopeia to about five times the distance between them, you will notice a bright star called Mirfak, which belongs to Perseus. Perseus is believed to be another Greek hero. Perseus has 2 bright stars, namely Mirfak and Algo. Note that Algo, which located at the southwest part almost forms a right-angled triangle with Mirfak and Almak of Andromeda. The star Mirfak actually marks the elbow of the hero while Algo represents part of the head of Medusa whom the hero has just slain.

In the Southern sky, there are not many bright stars. But don’t miss the magnificent Fomalhaut of Piscis Austrinus (Southern fish). It could be the brightest star in south sky in autumn. When you see Formalhaut rising in the South at the early evening, it is the season of deep autumn already.

Winter Sky

Orion, the Hunter, may be the most eye-catching constellation in winter.  There are seven bright stars can be found here, and they form the shape of an hourglass. The prominent part is his belt, where many people will see at the first glance. It is made up of 3 equally spaced bright star lining in a straight line. As the celestial equator passes through the belt, the figure lies with his head pointing North and the legs pointing South.

Just below the belt, there is a famous Nebula, namely M42 or the Orion Nebular. It is one of the few emission nebulae that can be seen with naked eye. It appears as a fuzzy illumination. It is seen under the telescope, you will see a greenish or gray glow around a central star, the famous Trapezium. Close by, just to the south, is the renowned Horsehead Nebula, a so-called dark nebula that is not visible in scopes but quite spectacular in long-exposure photographs.

When extended northward, the “Belt” points toward an orange star. This star names Aldebaran, is the eye of the Bull, Taurus. Taurus could be recognised by the V-shaped bull’s head with long horns tipped by 2 bright stars. This constellation denotes only the front half of the bull, and the rear part was believed to be submerges in the myth. When extending the line of the Belt and the eye of bull farther, you will pick out the famous Pleiades. Pleiades, or Seven Sisters (M46), is a nearby young galactic cluster. Seeing the members of it is a test for eyesight, as they are very close together. Actually, there are 7 apparently easy-to-see members. If it is seen under telescope, you will see dozens of blue-white gems, and the brighter ones surrounded with delicate stains of nebulosity.

In winter, there are several bright stars constituting the famous “winter Triangle”. The members of the triangle are Betelgeuse (at the shoulder of Orion), Procyon of Canis Minor, and Sirius of Canis Major. Canis Major also called the Great Dog, and it represents one of the Orion’s hunting dogs. It can be recognised by a prominent parallelogram of six stars forming 2 lines, the bottom one being a little curved. It contains a brilliant blue-white star (-1.5 magnitude), Sirius, which is the brightest stars in the sky. The Canis Minor, or Little Dog, was the second of Orion’s hunting dogs, and was always associated with him and the larger dog. It is tiny constellation but it can be picked out easily by the brilliant Procyon. Both Procyon and Sirius have a white dwarf neutron star as their companion. A white dwarf neutron star is very dense that a cubic centimeter material weighs more than a ton!