Spectroscopy and the Birth of Astrophysics

The 3D animation (above) depicts how the light of a distant star is studied by astronomers. The spectrum of the light provides vital information about the composition and history of stars. Now, let’s look into the history of stellar spectroscopy.

In 1802, William Wollaston noted that the spectrum of sunlight did not appear to be a continuous band of colours, but rather had a series of dark lines superimposed on it. Wollaston attributed the lines to natural boundaries between colours. Joseph Fraunhofer made a more careful set of observations of the solar spectrum in 1814 and found some 600 dark lines, and he specifically measured the wavelength of 324 of them. Many of the Fraunhofer lines in the solar spectrum retain the notations he created to designate them. In 1864, Sir William Huggins matched some of these dark lines in spectra from other stars with terrestrial substances, demonstrating that stars are made of the same materials of everyday material rather than exotic substances. This paved the way for modern spectroscopy.

Since even before the discovery of spectra, scientists had tried to find ways to categorize stars. By observing spectra, astronomers realized that large numbers of stars exhibit a small number of distinct patterns in their spectral lines. Classification by spectral features quickly proved to be a powerful tool for understanding stars.

The current spectral classification scheme was developed at Harvard Observatory in the early 20th century. Work was begun by Henry Draper who photographed the first spectrum of Vega in 1872. After his death, his wife donated the equipment and a sum of money to the Observatory to continue his work. The bulk of the classification work was done by Annie Jump Cannon from 1918 to 1924. The original scheme used capital letters running alphabetically, but subsequent revisions have reduced this as stellar evolution and typing has become better understood.

While the differences in spectra might seem to indicate different chemical compositions, in almost all instances, it actually reflects different surface temperatures. With some exceptions (e.g. the R, N, and S stellar types), material on the surface of stars is “primitive”: there is no significant chemical or nuclear processing of the gaseous outer envelope of a star once it has formed. Fusion at the core of the star results in fundamental compositional changes, but material does not generally mix between the visible surface of the star and its core. Ordered from highest temperature to lowest, the seven main stellar types are O, B, A, F, G, K, and M. Astronomers use one of several mnemonics to remember the order of the classification scheme. O, B, and A type stars are often referred to as early spectral types, while cool stars (G, K, and M) are known as late type stars.

Scientists assumed that the spectral classes represented a sequence of decreasing surface temperatures of the stars, but no one was able to demonstrate this quantitatively. Cecilia Payne, who studied the new science of quantum physics, knew that the pattern of features in the spectrum of any atom was determined by the configuration of its electrons. She showed that Cannon’s ordering of the stellar spectral classes was indeed a sequence of decreasing temperatures and she was able to calculate the temperatures.

  • More information: here

Credit: ESO, Jesse S. Allen

At the heart of most, if not all, giant galaxies lies a supermassive black hole. When dust and gas falls into the central black hole, it heats up and emits intense radiation. Quasars, some of the brightest objects in the cosmos, are powered by these phenomena. In these artist’s impressions of a quasar, the rotating ring of matter, and powerful jets of particles thrown out at close to the speed of light can be seen.

Credit: ESA/Hubble (M. Kornmesser)

M51: Chandra Captures Galaxy Sparkling in X-rays

Nearly a million seconds of observing time with NASA’s Chandra X-ray Observatory has revealed a spiral galaxy similar to the Milky Way glittering with hundreds of X-ray points of light.
The galaxy is officially named Messier 51 (M51) or NGC 5194, but often goes by its nickname of the “Whirlpool Galaxy.” Like the Milky Way, the Whirlpool is a spiral galaxy with spectacular arms of stars and dust. M51 is located about 30 million light years from Earth, and its face-on orientation to Earth gives us a perspective that we can never get of our own spiral galactic home.
By using Chandra, astronomers can peer into the Whirlpool to uncover things that can only be detected in X-rays. In this new composite image, Chandra data are shown in purple. Optical data from the Hubble Space Telescope are red, green, and blue.
Most of the X-ray sources are X-ray binaries (XRBs). These systems consist of pairs of objects where a compact star, either a neutron star or, more rarely, a black hole, is capturing material from an orbiting companion star. The infalling material is accelerated by the intense gravitational field of the compact star and heated to millions of degrees, producing a luminous X-ray source. The Chandra observations reveal that at least ten of the XRBs in M51 are bright enough to contain black holes. In eight of these systems the black holes are likely capturing material from companion stars that are much more massive than the Sun.

Credit: X-ray: NASA/CXC/Wesleyan Univ./R.Kilgard, et al; Optical: NASA/STScI

M51: Chandra Captures Galaxy Sparkling in X-rays

Nearly a million seconds of observing time with NASA’s Chandra X-ray Observatory has revealed a spiral galaxy similar to the Milky Way glittering with hundreds of X-ray points of light.

The galaxy is officially named Messier 51 (M51) or NGC 5194, but often goes by its nickname of the “Whirlpool Galaxy.” Like the Milky Way, the Whirlpool is a spiral galaxy with spectacular arms of stars and dust. M51 is located about 30 million light years from Earth, and its face-on orientation to Earth gives us a perspective that we can never get of our own spiral galactic home.

By using Chandra, astronomers can peer into the Whirlpool to uncover things that can only be detected in X-rays. In this new composite image, Chandra data are shown in purple. Optical data from the Hubble Space Telescope are red, green, and blue.

Most of the X-ray sources are X-ray binaries (XRBs). These systems consist of pairs of objects where a compact star, either a neutron star or, more rarely, a black hole, is capturing material from an orbiting companion star. The infalling material is accelerated by the intense gravitational field of the compact star and heated to millions of degrees, producing a luminous X-ray source. The Chandra observations reveal that at least ten of the XRBs in M51 are bright enough to contain black holes. In eight of these systems the black holes are likely capturing material from companion stars that are much more massive than the Sun.

Credit: X-ray: NASA/CXC/Wesleyan Univ./R.Kilgard, et al; Optical: NASA/STScI

How did scientists determine our location within the Milky Way galaxy—in other words, how do we know that our solar system is in the arm of a spiral galaxy, far from the galaxy’s center? 

There is no short answer to this question, because astronomers have followed many lines of evidence to determine the location of the solar system in the Milky Way. But some of the general techniques can be outlined briefly.
Finding one’s location in a cloud of a hundred billion stars—when one can’t travel beyond one’s own planet—is like trying to map out the shape of a forest while tied to one of the trees. One gets a rough idea of the shape of the Milky Way galaxy by just looking around—a ragged, hazy band of light circles the sky. It is about 15 degrees wide, and stars are concentrated fairly evenly along the strip. That observation indicates that our Milky Way Galaxy is a flattened disk of stars, with us located somewhere near the plane of the disk. Were it not a flattened disk, it would look different. For instance, if it were a sphere of stars, we would see its glow all over the sky, not just in a narrow band. And if we were above or below the disk plane by a substantial amount, we would not see it split the sky in half—the glow of the Milky Way would be brighter on one side of the sky than on the other.
The position of the sun in the Milky Way can be further pinned down by measuring the distance to all the stars we can see. In the late 18th century, astronomer William Herschel tried to do this, concluding that the earth was in the center of a ‘grindstone’-shaped cloud of stars. But Herschel was not aware of the presence of small particles of interstellar dust, which obscure the light from the most distant stars in the Milky Way. We appeared to be in the center of the cloud because we could see no further in all directions. To a person tied to a tree in a foggy forest, it looks like the forest stretches equally away in all directions, wherever one is.
A major breakthrough in moving the earth from the center of the galaxy to a point about 3/5 away from the edge came in the early decades of this century, when Harlow Shapley measured the distance to the large clusters of stars called globular clusters. He found they were distributed in a spherical distribution about 100,000 light-years in diameter, centered on a location in the constellation Sagittarius. Shapley concluded (and other astronomers have since verified) that the center of the distribution of globular clusters is the center of the Milky Way as well, so our galaxy looks like a flat disk of stars embedded in a spherical cloud, or ‘halo,’ of globular clusters.
In the past 75 years, astronomers have refined this picture, using a variety of techniques of radio, optical, infrared and even x-ray astronomy, to fill in the details: the location of spiral arms, clouds of gas and dust, concentrations of molecules and so on. The essential modern picture is that our solar system is located on the inner edge of a spiral arm, about 25,000 light-years from the center of the galaxy, which is in the direction of the constellation of Sagittarius.

Credit: Laurence A. Marschall in the department of physics at Gettysburg College

How did scientists determine our location within the Milky Way galaxy—in other words, how do we know that our solar system is in the arm of a spiral galaxy, far from the galaxy’s center?

There is no short answer to this question, because astronomers have followed many lines of evidence to determine the location of the solar system in the Milky Way. But some of the general techniques can be outlined briefly.

Finding one’s location in a cloud of a hundred billion stars—when one can’t travel beyond one’s own planet—is like trying to map out the shape of a forest while tied to one of the trees. One gets a rough idea of the shape of the Milky Way galaxy by just looking around—a ragged, hazy band of light circles the sky. It is about 15 degrees wide, and stars are concentrated fairly evenly along the strip. That observation indicates that our Milky Way Galaxy is a flattened disk of stars, with us located somewhere near the plane of the disk. Were it not a flattened disk, it would look different. For instance, if it were a sphere of stars, we would see its glow all over the sky, not just in a narrow band. And if we were above or below the disk plane by a substantial amount, we would not see it split the sky in half—the glow of the Milky Way would be brighter on one side of the sky than on the other.

The position of the sun in the Milky Way can be further pinned down by measuring the distance to all the stars we can see. In the late 18th century, astronomer William Herschel tried to do this, concluding that the earth was in the center of a ‘grindstone’-shaped cloud of stars. But Herschel was not aware of the presence of small particles of interstellar dust, which obscure the light from the most distant stars in the Milky Way. We appeared to be in the center of the cloud because we could see no further in all directions. To a person tied to a tree in a foggy forest, it looks like the forest stretches equally away in all directions, wherever one is.

A major breakthrough in moving the earth from the center of the galaxy to a point about 3/5 away from the edge came in the early decades of this century, when Harlow Shapley measured the distance to the large clusters of stars called globular clusters. He found they were distributed in a spherical distribution about 100,000 light-years in diameter, centered on a location in the constellation Sagittarius. Shapley concluded (and other astronomers have since verified) that the center of the distribution of globular clusters is the center of the Milky Way as well, so our galaxy looks like a flat disk of stars embedded in a spherical cloud, or ‘halo,’ of globular clusters.

In the past 75 years, astronomers have refined this picture, using a variety of techniques of radio, optical, infrared and even x-ray astronomy, to fill in the details: the location of spiral arms, clouds of gas and dust, concentrations of molecules and so on. The essential modern picture is that our solar system is located on the inner edge of a spiral arm, about 25,000 light-years from the center of the galaxy, which is in the direction of the constellation of Sagittarius.

Credit: Laurence A. Marschall in the department of physics at Gettysburg College

Coronal loop

The corona is the outer part of the solar atmosphere. Its name derives from the fact that, since it is extremely tenuous with respect to the lower atmosphere, it is visible in the optical band only during the solar eclipses as a faint crown (corona in Latin) around the black moon disk. When inspected through spectroscopy the corona reveals unexpected emission lines, which were first identified as due to a new element (coronium) but which were later ascertained to be due to high excitation states of iron. It became then clear that the corona is made of very high temperature gas, hotter than 1 MK(megakelvin). Almost all the gas is fully ionized there and thus interacts effectively with the ambient magnetic field. It is for this reason that the corona appears so inhomogeneous when observed in the X-ray band, in which plasma at million degrees emits most of its radiation. In particular, the plasma is confined inside magnetic flux tubes which are anchored on both sides to the underlying photosphere. When the confined plasma is heated more than the surroundings, its pressure and density increase. Since the tenuous plasma is optically thin, the intensity of its radiation is proportional to the square of the density, and the tube becomes much brighter than the surrounding ones and looks like a bright closed arch: a coronal loop.
Coronal Loops: Observations and Modeling of Confined Plasma

Credit: Fabio Reale

Coronal loop

The corona is the outer part of the solar atmosphere. Its name derives from the fact that, since it is extremely tenuous with respect to the lower atmosphere, it is visible in the optical band only during the solar eclipses as a faint crown (corona in Latin) around the black moon disk. When inspected through spectroscopy the corona reveals unexpected emission lines, which were first identified as due to a new element (coronium) but which were later ascertained to be due to high excitation states of iron. It became then clear that the corona is made of very high temperature gas, hotter than 1 MK(megakelvin). Almost all the gas is fully ionized there and thus interacts effectively with the ambient magnetic field. It is for this reason that the corona appears so inhomogeneous when observed in the X-ray band, in which plasma at million degrees emits most of its radiation. In particular, the plasma is confined inside magnetic flux tubes which are anchored on both sides to the underlying photosphere. When the confined plasma is heated more than the surroundings, its pressure and density increase. Since the tenuous plasma is optically thin, the intensity of its radiation is proportional to the square of the density, and the tube becomes much brighter than the surrounding ones and looks like a bright closed arch: a coronal loop.

Credit: Fabio Reale

Spiral galaxy ESO 137-001

This Hubble image shows ESO 137-001, a galaxy located in the southern constellation of Triangulum Australe (The Southern Triangle) — a delicate and beautiful spiral galaxy, but with a secret. The image not only captures the galaxy and its backdrop in stunning detail, but also something more dramatic — intense blue streaks streaming outwards from the galaxy, seen shining brightly in ultraviolet light.
These streaks are actually hot young stars, encased in wispy streams of gas that are being torn away from the galaxy by its surroundings as it moves through space. This violent galactic disrobing is due to a process known as ram pressure stripping — a drag force felt by an object moving through a fluid . The fluid in question here is superheated gas, which lurks at the centres of galaxy clusters.
This image combines NASA/ESA Hubble Space Telescope observations with data from the Chandra X-ray Observatory.

Credit: NASA, ESA, CXC

Spiral galaxy ESO 137-001

This Hubble image shows ESO 137-001, a galaxy located in the southern constellation of Triangulum Australe (The Southern Triangle) — a delicate and beautiful spiral galaxy, but with a secret. The image not only captures the galaxy and its backdrop in stunning detail, but also something more dramatic — intense blue streaks streaming outwards from the galaxy, seen shining brightly in ultraviolet light.

These streaks are actually hot young stars, encased in wispy streams of gas that are being torn away from the galaxy by its surroundings as it moves through space. This violent galactic disrobing is due to a process known as ram pressure stripping — a drag force felt by an object moving through a fluid . The fluid in question here is superheated gas, which lurks at the centres of galaxy clusters.

This image combines NASA/ESA Hubble Space Telescope observations with data from the Chandra X-ray Observatory.

Credit: NASA, ESA, CXC

Accretion Disks

Accretion flows are ubiquitous in astrophysics: they occur around protostars, accreting compact objects in binary systems, and supermassive black holes at the cores of galaxies. Much of professor James M. Stone's work has concerned studies of the local hydrodynamic and magnetohydrodynamics (MHD) processes that can lead to outward angular momentum transport in accretion disks. As computers become more powerful, previous studies of local patches of an accretion flow are being expanded into global studies that encompass the entire disk.

Accretion flows that cannot cool via emission of radiation become vertically thick and nearly spherical. Thus, they are intrinsically multidimensional. To study the structure and evolution of non-radiative accretion flows, 2D (axisymmetric) hydrodynamical simulations were performed using a non-uniform grid that spanned more than two decades in radius.

The most striking property of the flow is the large fluctuations produced by strong convection. Convective eddies transport a lot of mass both inwards and outwards, but the net mass accretion rate is very small and set by the properties of the flow near the inner boundary. A vanishingly small accretion rate may help to explain the deficit of high energy emission observed from accreting compact sources.

While understanding the properties of hydrodynamical accretion flows is important, it is generally agreed that angular momentum transport is in fact mediated by magnetic stresses. Thus, repeating the global simulations of non-radiative accretion flows with MHD calculations is vital.

Credit: James M. Stone

Plasmoids

A plasmoid is a coherent structure of plasma and magnetic fields. Plasmoids have been proposed to explain natural phenomena such as ball lightning, magnetic bubbles in the magnetosphere, and objects in cometary tails, in the solar wind, in the solar atmosphere, and in the heliospheric current sheet. Plasmoids produced in the laboratory include field-reversed configurations, spheromaks, and in dense plasma focuses.

The word plasmoid was coined in 1956 by Winston H. Bostick (1916-1991) to mean a “plasma-magnetic entity”. Bostick went on to apply his theory of plasmoids to astrophysics phenomena. 

Active regions on the solar surface are often the site of eruptions. These are associated with magnetic fields from the solar interior rising to the surface and gradually expanding into the Sun’s outer atmosphere, the corona, in a process known as magnetic flux emergence.

A group of scientists from the University of St Andrews developed 3D computer models of these phenomena, revealing that the emergence of magnetic flux naturally leads to the formation and expulsion of plasmoids that adopt a twisted tube configuration.

The formation of the plasmoids is due to the motion of plasma in the lower atmosphere of the Sun. These motions bring magnetic fieldlines closer together to reconnect and build a new magnetic flux system (i.e. the plasmoid). Whether the plasmoids are ‘failed’ or ‘successful’ (i.e. they erupt into space) depends on the level of interaction between the new emerging field and the old, pre-existing magnetic field in the solar corona.

Credit: Vasilis Archontis

The Submillimeter Array telescope unveils how small cosmic seeds grow into big stars

New images from the Smithsonian’s Submillimeter Array (SMA) telescope provide the most detailed view yet of stellar nurseries within the Snake Nebula. These images offer new insights into how cosmic seeds can grow into massive stars.
Stretching across almost 100 light-years of space, the Snake Nebula is located about 11,700 light-years from Earth in the direction of the constellation Ophiuchus. In images from NASA’s Spitzer Space Telescope, it appears as a sinuous dark tendril against the starry background. It was targeted because it shows the potential to form many massive stars (stars heavier than eight times our Sun).
Full Article

Image Credit: Spitzer/GLIMPSE/MIPS, Herschel/HiGal, Ke Wang (ESO)

The Submillimeter Array telescope unveils how small cosmic seeds grow into big stars

New images from the Smithsonian’s Submillimeter Array (SMA) telescope provide the most detailed view yet of stellar nurseries within the Snake Nebula. These images offer new insights into how cosmic seeds can grow into massive stars.

Stretching across almost 100 light-years of space, the Snake Nebula is located about 11,700 light-years from Earth in the direction of the constellation Ophiuchus. In images from NASA’s Spitzer Space Telescope, it appears as a sinuous dark tendril against the starry background. It was targeted because it shows the potential to form many massive stars (stars heavier than eight times our Sun).

Full Article

Image Credit: Spitzer/GLIMPSE/MIPS, Herschel/HiGal, Ke Wang (ESO)

 The Bolshoi Simulation

What if you could fly through the universe and see dark matter? While the technology for taking such a flight remains under development, the technology for visualizing such a flight has taken a grand leap forward with the completion of the Bolshoi Cosmological Simulation.
After 6 million CPU hours, the world’s seventh fastest supercomputer output many scientific novelties including the above flight simulation. Starting from the relatively smooth dark matter distribution of the early universe discerned from the microwave background and other large sky data sets, the Bolshoi tracked the universe’s evolution to the present epoch shown above, given the standard concordance cosmology. The bright spots in the simulation above are all knots of normally invisible dark matter, many of which contain normal galaxies. Long filaments and clusters of galaxies, all gravitationally dominated by dark matter, become evident.
Statistical comparison between the Bolshoi and current real sky maps of actual galaxies show good agreement. Although the Bolshoi simulation bolsters the existence of dark matter, many questions about our universe remain, including the composition of dark matter, the nature of dark energy, and how the first generation of stars and galaxies formed.
For more information about the Bolshoi Cosmological Simulation, click here.

Credit:  A. Klypin (NMSU), J. Primack (UCSC) et al., Chris Henze (NASA Ames), NASA’s Pleiades Supercomputer

The Bolshoi Simulation

What if you could fly through the universe and see dark matter? While the technology for taking such a flight remains under development, the technology for visualizing such a flight has taken a grand leap forward with the completion of the Bolshoi Cosmological Simulation.

After 6 million CPU hours, the world’s seventh fastest supercomputer output many scientific novelties including the above flight simulation. Starting from the relatively smooth dark matter distribution of the early universe discerned from the microwave background and other large sky data sets, the Bolshoi tracked the universe’s evolution to the present epoch shown above, given the standard concordance cosmology. The bright spots in the simulation above are all knots of normally invisible dark matter, many of which contain normal galaxies. Long filaments and clusters of galaxies, all gravitationally dominated by dark matter, become evident.

Statistical comparison between the Bolshoi and current real sky maps of actual galaxies show good agreement. Although the Bolshoi simulation bolsters the existence of dark matter, many questions about our universe remain, including the composition of dark matter, the nature of dark energy, and how the first generation of stars and galaxies formed.

  • For more information about the Bolshoi Cosmological Simulation, click here.

Credit: A. Klypin (NMSU), J. Primack (UCSC) et al., Chris Henze (NASA Ames), NASA’s Pleiades Supercomputer

What is a gamma-ray burst?

Gamma-ray bursts (GRBs) are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the brightest electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes. The initial burst is usually followed by a longer-lived “afterglow” emitted at longer wavelengths (X-ray, ultraviolet, optical, infrared, microwave and radio).
Most observed GRBs are believed to consist of a narrow beam of intense radiation released during a supernova or hypernova as a rapidly rotating, high-mass star collapses to form a neutron star, quark star, or black hole. A subclass of GRBs (the “short” bursts) appear to originate from a different process - this may be due to the merger of binaryneutron stars. The cause of the precursor burst observed in some of these short events may be due to the development of a resonance between the crust and core of such stars as a result of the massive tidal forces experienced in the seconds leading up to their collision, causing the entire crust of the star to shatter.
Gamma-ray bursts are thought to be highly focused explosions, with most of the explosion energy collimated into a narrow jet traveling at speeds exceeding 99.995% of the speed of light. The approximate angular width of the jet (that is, the degree of spread of the beam) can be estimated directly by observing the achromatic “jet breaks” in afterglow light curves: a time after which the slowly decaying afterglow begins to fade rapidly as the jet slows and can no longer beam its radiation as effectively

Image credit: NASA/Swift/Cruz deWilde

What is a gamma-ray burst?

Gamma-ray bursts (GRBs) are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the brightest electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes. The initial burst is usually followed by a longer-lived “afterglow” emitted at longer wavelengths (X-ray, ultraviolet, optical, infrared, microwave and radio).

Most observed GRBs are believed to consist of a narrow beam of intense radiation released during a supernova or hypernova as a rapidly rotating, high-mass star collapses to form a neutron star, quark star, or black hole. A subclass of GRBs (the “short” bursts) appear to originate from a different process - this may be due to the merger of binaryneutron stars. The cause of the precursor burst observed in some of these short events may be due to the development of a resonance between the crust and core of such stars as a result of the massive tidal forces experienced in the seconds leading up to their collision, causing the entire crust of the star to shatter.

Gamma-ray bursts are thought to be highly focused explosions, with most of the explosion energy collimated into a narrow jet traveling at speeds exceeding 99.995% of the speed of light. The approximate angular width of the jet (that is, the degree of spread of the beam) can be estimated directly by observing the achromatic “jet breaks” in afterglow light curves: a time after which the slowly decaying afterglow begins to fade rapidly as the jet slows and can no longer beam its radiation as effectively

Image credit: NASA/Swift/Cruz deWilde

Pulsar kick

A pulsar kick is the phenomenon that a neutron star often does not move with the velocity of its progenitor star (the origin star of a supernova explosion), but rather with a substantially greater speed. The cause of pulsar kicks is unknown, but many astrophysicists believe that it must be due to an asymmetry in the way a supernova explodes.
It is generally accepted today that the average pulsar kick ranges from 200–500 km/s. However, some pulsars have a much greater velocity. For example, the hypervelocity star B1508+55 has been reported to have a speed of 1100 km/s and a trajectory leading it out of the galaxy.
An extremely convincing example of a pulsar kick can be seen in the Guitar Nebula, where the bow shock - generated by the pulsar B2224+65, is moving relative to the supernova remnant nebula has been observed and confirms a velocity of 800 km/s. The Guitar Nebula is a stellar corpse that is tearing through interstellar gas and creating a guitar-shaped wake of hot hydrogen.

Pulsar kick

A pulsar kick is the phenomenon that a neutron star often does not move with the velocity of its progenitor star (the origin star of a supernova explosion), but rather with a substantially greater speed. The cause of pulsar kicks is unknown, but many astrophysicists believe that it must be due to an asymmetry in the way a supernova explodes.

It is generally accepted today that the average pulsar kick ranges from 200–500 km/s. However, some pulsars have a much greater velocity. For example, the hypervelocity star B1508+55 has been reported to have a speed of 1100 km/s and a trajectory leading it out of the galaxy.

An extremely convincing example of a pulsar kick can be seen in the Guitar Nebula, where the bow shock - generated by the pulsar B2224+65, is moving relative to the supernova remnant nebula has been observed and confirms a velocity of 800 km/s. The Guitar Nebula is a stellar corpse that is tearing through interstellar gas and creating a guitar-shaped wake of hot hydrogen.

Binary star

A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star or secondary.

Binary stars are often detected optically, in which case they are called visual binaries. Many visual binaries have long orbital periods of several centuries or millennia and therefore have orbits which are uncertain or poorly known. They may also be detected by indirect techniques, such as spectroscopy (spectroscopic binaries) or astrometry (astrometric binaries). If a binary star happens to orbit in a plane along our line of sight, its components will eclipse and transit each other; these pairs are called eclipsing binaries, or, as they are detected by their changes in brightness during eclipses and transits, photometric binaries.

The first GIF shows an artist’s impression of an eclipsing binary star system. As the two stars orbit each other they pass in front of one another and their combined brightness, seen from a distance, decreases. 

Algol, known colloquially as the Demon Star, is a bright star in the constellation Perseus. It is one of the best known eclipsing binaries, (2nd GIF) although Algol is actually a three-star system (Beta Persei A, B, and C) in which the large and bright primary Beta Persei A is regularly eclipsed by the dimmer Beta Persei B.

The second animation was assembled from 55 images of the CHARA interferometer in the near-infrared H-band, sorted according to orbital phase.

Image credit: ESO/CHARA

Supernova explosion (artist’s impression) 

One of the most massive cosmic explosive events in the universe is a supernova. A supernova is the violent death of a luminous supergiant star. These blindingly bright star bursts occur at the end of a star’s lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy.
If the star is particularly massive, then its core will collapse and in so doing will release a huge amount of energy. This will cause a blast wave that ejects the star’s envelope into interstellar space. Astronomers originally classified supernovae into two “types”, I and II. Type I had no hydrogen emission lines in their spectra whereas Type II exhibited hydrogen emission lines. Later it was realized that there were in fact three quite distinct Type I supernovae, now labelled Type Ia, Type Ib and Type Ic.
Supernovae play a fundamental role in a great cosmic recycling program. We believe that almost all of the elements in the Universe that are heavier than hydrogen and helium are created either in the centres of stars during their lifetimes or in the supernova explosions that mark the demise of larger stars.


Image Credit: freeara

Supernova explosion (artist’s impression)

One of the most massive cosmic explosive events in the universe is a supernova. A supernova is the violent death of a luminous supergiant star. These blindingly bright star bursts occur at the end of a star’s lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy.

If the star is particularly massive, then its core will collapse and in so doing will release a huge amount of energy. This will cause a blast wave that ejects the star’s envelope into interstellar space. Astronomers originally classified supernovae into two “types”, I and II. Type I had no hydrogen emission lines in their spectra whereas Type II exhibited hydrogen emission lines. Later it was realized that there were in fact three quite distinct Type I supernovae, now labelled Type Ia, Type Ib and Type Ic.

Supernovae play a fundamental role in a great cosmic recycling program. We believe that almost all of the elements in the Universe that are heavier than hydrogen and helium are created either in the centres of stars during their lifetimes or in the supernova explosions that mark the demise of larger stars.


Image Credit: freeara


XZ Tauri is a binary system approximately 450 light-years away in the constellation Taurus. The system is composed of two T Tauri stars orbiting each other about 6 billion kilometers apart (roughly the same distance as Pluto is from the Sun). The system made news in 2000 when a superflare was observed in the system.

Image credit: NASA, ESA and J. Schmidt

XZ Tauri is a binary system approximately 450 light-years away in the constellation Taurus. The system is composed of two T Tauri stars orbiting each other about 6 billion kilometers apart (roughly the same distance as Pluto is from the Sun). The system made news in 2000 when a superflare was observed in the system.

Image credit: NASA, ESA and J. Schmidt