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Can stars be observed from space by x-rays, near infrared and radio wavelengths?
Yes, and not only from space but from the Earth surface too. Stars emit in almost all wavelengths depending on their surface temperatures. The hotter the star is the shorter (higher energy) wavelengths it'll emit.
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Merging Black Holes Observed in New Detail
Scientists have pinpointed the precise locations of a pair of supermassive black holes at the centers of two colliding galaxies 300 million light-years away.
Infrared images made by the Keck II telescope in Hawaii reveal the two black holes at the center of the galaxy merger known as NGC 6240 are each surrounded by a rotating disk of stars and cloudy stellar nurseries.
The new images are detailed in Science Express, an online publication of the journal Science.
Cosmic train wreck
Scientists had previously observed NGC 6240 in a piecemeal fashion, using different wavelengths of light. Images captured by the Hubble Space Telescope showed the outer parts of the colliding galaxies in visible light, and revealed long tidal tails made of orphaned stars, gas, and dust.
Subsequent X-ray observations by NASA&rsquos Chandra X-ray Observatory revealed the presence of two supermassive black holes at the center of each galaxy, and the Very Long Baseline Array spotted two radio sources in the galaxies&rsquo central regions. The problem was combining all of the images to form a single coherent picture.
&ldquoYou have all these different telescopes and they look at the same piece of sky but see wildly different things,&rdquo said study team member Willem de Vries of the University of California, Davis.
Keck II uses a relatively new type of imaging called adaptive optics, which uses an artificial laser-generated "guide star" as a reference and a rapidly deforming mirror to correct image distortions from the Earth's atmosphere in real time.
The Keck II images were of such high spatial resolution that scientists could identify features in NGC 6240 captured by the other telescopes in the optical, X-ray and radio wavelengths.
Like a Rosetta Stone, the Keck II images allowed scientists for the first time to calibrate the different images of NGC 6420.
&ldquoNow we can really see it all&mdashthe hot dust in the infrared, the stars in the visible and infrared, and the X-rays and radio emissions from right around the black holes,&rdquo said study leader Claire Max at the University of California, Santa Cruz.
Scientists think galactic mergers are one of the primary ways galaxies form. Like heated wax in a lava lamp, two small galaxies can come together to form one larger one, or a blob of gas and stars might pinch off during a particularly messy galactic smash-up and, over cosmic time, the result evolves into a diminutive dwarf galaxy.
Our own Milky Way galaxy is expected to collide and merge with its neighbor Andromeda in a few billion years to form a large elliptical galaxy some scientists jokingly call &ldquoMilkomeda&rdquo or &ldquoAndromeda Way.&rdquo When that occurs, a black hole merger similar to that of NGC 6420 could occur.
&ldquoWe have a wimpier black hole than the two galaxies [in NGC 6420], but we have a black hole and we believe Andromeda does too,&rdquo Max told SPACE.com.
When galaxies merge, the behemoth black holes at their centers merge and grow as well. Recent studies have shown that supermassive black holes help determine many properties of their host galaxies. Scientists say this idea, sometimes called &ldquoco-evolution,&rdquo is among the most surprising realizations to emerge from astronomy in recent years.
&ldquoThe gravitational influence of the black hole is actually limited to a relatively small region right around it, so how can it affect the rest of the galaxy?&rdquo Max said. &ldquoBut if the black hole and the galaxy around it evolved together through the same sequence of merger events, that would explain the correlations.&rdquo
Scientists estimate the two black holes in NGC 6240 will spiral into each other and merge in 10 million to 100 million years.
Observations: Seeing in X-ray wavelengths
X-rays are the signatures of the high-energy Universe. Any object heated to more than a million degrees Celsius will begin to give off significant quantities of X-rays. This is around the temperature of the Sun’s outer atmosphere, known as the corona. It is therefore no surprise that X-ray astronomy began with studies of the Sun before detections of other X-ray objects elsewhere in the Universe were made.
X-rays are completely absorbed by the atmosphere of the Earth, so satellites are the only way of collecting this radiation. During the 1970s, satellites discovered hundreds of powerful X-ray sources in our galaxy.
They are more powerful that the Sun’s emission and, in many case, seem to be coming from binary stars. These are not ordinary binary systems, however. Instead, one member is a dead stellar core, known as a neutron star, which is ripping gas from the ordinary star.
As the gas spirals through the strong gravitational field of the neutron star, creating a surrounding disc, it heats up enormously and starts sending X-rays into space.
Some X-ray sources are even more intense and astronomers think that these are systems in which a black hole, with its even stronger gravitational field, is replacing the neutron star. The most famous of these black hole candidates is Cygnus X-1 – so famous, in fact, that rock songs have been written about it!
Supernova remnants are emitters of X-rays as well as ultraviolet. Beyond our galaxy, much larger black holes power the tremendous X-ray output of active galaxies. The flickering of this emission can be used to prove that the heart of an active galaxy must only be about the size of our Solar System, increasing the belief that a black hole is responsible.
Now, ESA’s X-ray observatory XMM-Newton is sensitive enough to detect the X-rays coming from the atmospheres of normal stars. It can also clearly see the X-rays coming from the gas in clusters of galaxies, making it an excellent tool with which to search for distant, as yet undiscovered, galaxy clusters.
NASA's Top 10 Gamma-Ray Sources in the Universe
Gamma-rays are the highest-energy form of light in the universe. Some are generated by transient events, such as solar flares and the huge star explosions known as supernovas. Others are produced by steady sources like the supermassive black holes at the hearts of galaxies.
NASA's Fermi Gamma-ray Space Telescope has been mapping out the high-energy sky since its June 2008 launch. Earlier this year, the Fermi team released its second catalog of sources detected by the instrument's Large Area Telescope (LAT), producing an inventory of 1,873 objects shining in gamma-ray light.
Fermi scientists recently compiled a "top 10 list" to mark the occasion, and to highlight the diversity of gamma-ray sources. Five of the sources on the list are found within our own Milky Way, while the other five reside in distant galaxies.
Fermi's top five sources within our galaxy are:
1. The Crab Nebula: The famous Crab Nebula, located in the constellation Taurus, is the wreckage of an exploded star whose light reached Earth in 1054. Located 6,500 light-years away, the Crab is one of the most-studied objects in the sky. [Supernovas: Photos of Star Explosions]
At the heart of an expanding gas cloud lies what's left of the original star's core, a super-dense neutron star (also called a pulsar) that spins 30 times per second. Until recently, all of the Crab's high-energy emissions were thought to be the result of physical processes near the pulsar that tapped into this rapid spin.
For decades, most astronomers regarded the Crab Nebula as a super-steady beacon at X-ray energies. But data from several orbiting instruments &mdash including Fermi's Gamma-ray Burst Monitor &mdash now show unexpected variations. Astronomers have demonstrated that since 2008, the nebula has faded by 7 percent at high energies, a reduction likely tied to the environment around its central neutron star.
Since 2007, Fermi and the Italian Space Agency's AGILE satellite have detected several short-lived gamma-ray flares at energies hundreds of times higher than the nebula's observed X-ray variations. In April, the satellites detected two of the most powerful gamma-ray flares yet recorded.
To account for these "superflares," scientists say that electrons near the pulsar must be accelerated to energies a thousand trillion times greater than that of visible light. That's far beyond what can be achieved by the Large Hadron Collider near Geneva, Switzerland, now the most powerful particle accelerator on Earth. [Twisted Physics: 7 Mind-Blowing Findings]
2. W44:Another interesting supernova remnant detected by Fermi is W44. Thought to be about 20,000 years old &mdash middle-aged for a such a structure &mdash W44 is located 9,800 light-years away in the constellation Aquila.
The LAT not only detects this W44, it actually reveals super-energetic gamma-rays coming from places where the remnant's expanding shock wave is known to be interacting with cold, dense gas clouds.
Such observations are important in solving a long-standing problem in astrophysics: the origin of cosmic rays. Cosmic rays are particles, primarily protons, that move through space at nearly the speed of light. Magnetic fields deflect the particles as they race across the galaxy, and this interaction scrambles their path and masks their origins.
Scientists can't say for sure where the highest-energy cosmic rays come from, but they regard supernova remnants as perhaps their likliest origin.
In 1949, the Fermi telescope's namesake, physicist Enrico Fermi, suggested that the highest-energy cosmic rays were accelerated in the magnetic fields of gas clouds. In the decades that followed, astronomers showed that the magnetic fields in the expanding shock wave of a supernova remnant are just about the best location for this process to work.
So far, LAT observations of W44 and several other remnants strongly suggest that the gamma-ray emission arises from accelerated protons as they collide with gas atoms.
3. V407 Cygni: V407 Cygni is a so-called symbiotic binary system &mdash one that contains a compact white dwarf and a red giant star that has swollen to about 500 times the size of the sun.
V407 Cyni lies about 9,000 light-years away in the constellation Cygnus. The system occasionally flares up when gas from the red giant accumulates on the dwarf's surface and eventually explodes. This event is sometimes called a nova (after a Latin term meaning "new star").
When the system's most recent eruption occurred in March 2010, Fermi's LAT surprised many scientists by detecting the nova as a brilliant source. Scientists didn't expect that this type of outburst had the power to produce high-energy gamma-rays.
4. Pulsar PSR J0101-6422: Pulsars &mdash rapidly rotating neutron stars &mdash constitute about 6 percent of the new catalog. In some cases the LAT can detect gamma-ray pulses directly, but in many cases pulses were first found at radio wavelengths based on suspicions that a faint LAT source might be a pulsar.
PSR J0101-6422 is located in the southern constellation of Tucana, its quirky name reflecting its position in the sky.
The Fermi team originally took notice of the object as a fairly bright but unidentified gamma-ray source in an earlier LAT catalog. Because the distribution of gamma-ray energies in the source resembled what is normally seen in pulsars, radio astronomers in Australia took a look at it using their Parkes radio telescope.
Pulsars are neutron stars, compact objects packing more mass than the sun's into a sphere roughly the size of Washington, D.C. Lighthouse-like beams of radiation powered by the pulsar's rapid rotation and strong magnetic field sweep across the sky with every spin, and astronomers can detect these beams if they happen to sweep toward Earth.
The Parkes study found radio signals from a pulsar rotating at nearly 400 times a second &mdash comparable to the spin of a kitchen blender &mdash at the same position as the unknown Fermi source. With this information, the LAT team was able to discover that PSR J0101-6422 also blinks in gamma-rays at the same incredible rate.
5. 2FGL J0359.5+5410: Fermi scientists don't know what to make of this source, which is located in the constellation Camelopardalis. It resides near the populous midplane of our galaxy, which increases the chance that it's actually an object in the Milky Way.
While its gamma-ray spectrum resembles that of a pulsar, pulsations have not been detected, and it isn't associated with a known object at other wavelengths.
The top five sources beyond the Milky Way are:
1. Centaurus A:The giant elliptical galaxy NGC 5128 is located 12 million light-years away in the southern constellation Centaurus. One of the closest active galaxies, it hosts the bright radio source designated Cen A. Much of the radio emission arises from lobes of gas a million light-years wide, which have been hurled out by the supermassive black hole at the galaxy's center. [Photos: Black Holes of the Universe]
Fermi's LAT detects high-energy gamma-rays from an extended region around the galaxy that corresponds to the radio-emitting lobes. The radio emission comes from fast-moving particles. When a lower-energy photon collides with one of these particles, the photon receives a kick that boosts its energy into the gamma-ray regime.
It's a process that sounds more like billiards than astrophysics, but Fermi's LAT shows that it's happening in Cen A.
2. The Andromeda Galaxy (M31): At a distance of 2.5 million light-years, the Andromeda Galaxy is the nearest spiral galaxy to us, one of similar size and structure as our own Milky Way. Easily visible to the naked eye in a dark sky, it's also a favorite target of sky gazers.
The LAT team expected to detect M31 because it's so similar to our own galaxy, which sports a bright band of diffuse emission that creates the most prominent feature in the gamma-ray sky. These gamma-rays are mostly produced when high-energy cosmic rays smash into the gas between stars.
"It took two years of LAT observations to detect M31," Jürgen Knödlseder at the Research Institute for Astrophysics and Planetology in Toulouse, France, said in a statement. Currently a visiting scientist at the SLAC National Accelerator Laboratory in California, he worked on the M31 study.
"We concluded that the Andromeda Galaxy has fewer cosmic rays than our own Milky Way, probably because M31 forms stars &mdash including those that die as supernovae, which help produce cosmic rays &mdashmore slowly than our galaxy," Knödlseder added.
3. The Cigar Galaxy (M82): What works for the Andromeda Galaxy works even better for M82, a so-called starburst galaxy that is also a favorite of amateur astronomers. M82 is located 12 million light-years away in the constellation Ursa Major.
M82's central region forms young stars at a rate some 10 times higher than the Milky Way does, activity that also guarantees a high rate of supernovae as the most short-lived stars come to explosive ends.
Eventually, M82's superpowered star formation will subside as the gas needed to make new stars is consumed, but that may be tens of millions of years in the future. For now, it's a bright source of gamma-rays for Fermi.
4. Blazar PKS 0537-286: At the core of an active galaxy is a massive black hole that drives jets of particles moving near the speed of light. Astronomers call the galaxy a blazar when one of these jets is pointed our way &mdash the best view for seeing dramatic flares as conditions change within the jet. [Video: Of Blazars and Black Holes]
PKS 0537-286 is a variable blazar in the constellation Leo and the second most distant LAT object. Astronomers have determined that the galaxy lies more than 11.7 billion light-years away.
The blazar is the farthest active galaxy in the Fermi catalog to show variability. Astronomers are witnessing changes in the jet powered by this galaxy's supermassive black hole that occurred when the universe was just 2 billion years old (it is now about 13.7 billion years old).
5. 2FGL J1305.0+1152: The last item is another mystery object, one located in the constellation Virgo and high above our galaxy's midplane. It remains faint even after two years of LAT observations.
One clue to classifying these objects lies in their gamma-ray spectrum &mdash that is, the relative number of gamma-rays seen at different energies. At some energy, the spectra of many objects display what astronomers call a "spectral break," a greater-than-expected drop-off in the number of gamma-rays seen at increasing energies.
If this object were a pulsar, it would show a fast cutoff at higher energies. Many blazars exhibit much more gradual cutoffs. But 2FGL J1305.0+1152 shows no evidence of a spectral break at all, leaving its nature a true mystery &mdash for now, anyway.
Can stars be observed from space by x-rays, near infrared and radio wavelengths? - Astronomy
Lecture 11: More on Telescopes: X-ray and Radio Telescopes, Telescopes in Space
Because of angular resolution problems at radio wavelengths (recall the equation for resolving power from Lecture 10), radio telescopes are typically very large compared to visible light telescopes.
For example to resolve the star and planet discussed in Lecture 10, a radio telescope operating at a wavelength of 10 centimeters would have to have a diameter of
Clearly a single telescope of this size cannot be built for finite sums of money!
Radio astronomers instead have adopted a strategy of building interferometers where practical size telescopes are built and spaced at distances as large as the diameter of the Earth. The outputs of the telescopes are combined to synthesize the angular resolution of a much larger telescope. The separation of the telescopes is equivalent to the diameter of a single telescope and is frequently referred to as the "baseline". Note that this interferometric style of telescope can vastly improve the angular resolution of a telescope but the light gathering power is just the sum of the areas of the individual telescopes.
The VLA . Very Large Array, in Socorro, New Mexico, is an example of a radio telescope built on interferometric principles.
The VLBA = Very Large Baseline Array couples telescopes spread across nearly the earth's diameter:
So far we have seen that 1) reflecting telescopes are used over a much broader range of wavelengths than refractors, and 2) radio telescopes are reflectors but are generally much larger than visible light telescopes because of the longer wavelength of radio waves.
Underlying much of the discussion of different types of telescopes is the value of observing objects at different wavelengths. Each regime of the electromagnetic spectrum can contribute to understanding a particular object, but we can also categorize various parts of the electromagnetic spectrum as being the optimum range for studying particular phenomena:
Notice the importance of temperature in the above table -- relation between wavelength of maximum output and temperature is the governing principle!
Astronomers See Distant Eruption as Black Hole Destroys Star
For the first time, astronomers have directly imaged the formation and expansion of a fast-moving jet of material ejected when a supermassive black hole ripped apart a star.
For the first time, astronomers have directly imaged the formation and expansion of a fast-moving jet of material ejected when the powerful gravity of a supermassive black hole ripped apart a star that wandered too close to the massive monster.
The scientists tracked the event with radio and infrared telescopes, including the National Science Foundation's Very Long Baseline Array (VLBA) and NASA's Spitzer Space Telescope, in a pair of colliding galaxies called Arp 299. The galaxies are nearly 150 million light-years from Earth. At the core of one of the galaxies, a black hole 20 million times more massive than the Sun shredded a star more than twice the Sun's mass, setting off a chain of events that revealed important details of the violent encounter. The researchers also used observations of Arp 299 made by NASA's Hubble space telescope prior to and after the appearance of the eruption.
Only a small number of such stellar deaths, called tidal disruption events, or TDEs, have been detected. Theorists have suggested that material pulled from the doomed star forms a rotating disk around the black hole, emitting intense X-rays and visible light, and also launches jets of material outward from the poles of the disk at nearly the speed of light.
"Never before have we been able to directly observe the formation and evolution of a jet from one of these events," said Miguel Perez-Torres, of the Astrophysical Institute of Andalucia in Granada, Spain, and an author on a paper describing the finding.
The first indication came on January 30, 2005, when astronomers using the William Herschel Telescope in the Canary Islands discovered a bright burst of infrared emission coming from the nucleus of one of the colliding galaxies in Arp 299. On July 17, 2005, the VLBA revealed a new, distinct source of radio emission from the same location.
"As time passed, the new object stayed bright at infrared and radio wavelengths, but not in visible light and X-rays," said Seppo Mattila, of the University of Turku in Finland, another author on the new paper. "The most likely explanation is that thick interstellar gas and dust near the galaxy's center absorbed the X-rays and visible light, then re-radiated it as infrared." The researchers used the Nordic Optical Telescope on the Canary Islands and NASA's Spitzer to follow the object's infrared emission.
Continued observations with the VLBA, the European VLBI Network (EVN), and other radio telescopes, carried out over nearly a decade, showed the source of radio emission expanding in one direction, just as expected for a jet. The measured expansion indicated that the material in the jet moved at an average of one-fourth the speed of light. The radio waves are not absorbed by the dust, but pass through it.
These observations used multiple radio-telescope antennas, separated by thousands of miles, to gain the resolving power, or ability to see fine detail, required to detect the expansion of an object so distant.
Most galaxies have supermassive black holes, containing millions to billions of times the mass of the Sun, at their cores. In a black hole, the mass is so concentrated that its gravitational pull is so strong that not even light can escape. When those supermassive black holes are actively drawing in material from their surroundings, that material forms a rotating disk around the black hole, and super-fast jets of particles are launched outward. This is the phenomenon seen in radio galaxies and quasars.
"Much of the time, however, supermassive black holes are not actively devouring anything, so they are in a quiet state," Perez-Torres explained. "Tidal disruption events can provide us with a unique opportunity to advance our understanding of the formation and evolution of jets in the vicinities of these powerful objects."
"Because of the dust that absorbed any visible light, this particular tidal disruption event may be just the tip of the iceberg of what until now has been a hidden population," Mattila said. "By looking for these events with infrared and radio telescopes, we may be able to discover many more, and learn from them."
Such events may have been more common in the distant universe, so studying them may help scientists understand the environment in which galaxies developed billions of years ago.
The discovery, the scientists said, came as a surprise. The initial infrared burst was discovered as part of a project that sought to detect supernova explosions in such colliding pairs of galaxies. Arp 299 has seen numerous stellar explosions, and has been dubbed a "supernova factory." This new object originally was considered to be a supernova explosion. Only in 2011, six years after discovery, the radio-emitting portion began to show an elongation. Subsequent monitoring showed the expansion growing, confirming that what the scientists are seeing is a jet, not a supernova.
Mattila and Perez-Torres led a team of 36 scientists from 26 institutions around the world in the observations of Arp 299. They published their findings in the June 14 issue of the journal Science.
The Long Baseline Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. NASA's Jet Propulsion Laboratory, Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for NASA.
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.
Infrared Radiation - Warmth From The Cold of Space
The light we see with our eyes is really a very small portion of what is called the "Electromagnetic Spectrum." The Electromagnetic Spectrum includes all types of radiation - from the X-rays used at hospitals, to radio waves used for communication, and even the microwaves you cook food with.
Radiation in the Electromagnetic Spectrum is often categorized by wavelength. Short wavelength radiation is of the highest energy and can be very dangerous - Gamma, X-rays and ultraviolet are examples of short wavelength radiation. Longer wavelength radiation is of lower energy and is usually less harmful - examples include radio, microwaves and infrared. A rainbow shows the optical (visible) part of the Electromagnetic Spectrum and infrared (if you could see it) would be located just beyond the red side of the rainbow.
Although infrared radiation is not visible, humans can sense it - as heat. Put your hand next to a hot oven if you want to experience infrared radiation "first-hand!
Why study Infrared Radiation from space?
Astronomers have found that infrared radiation is especially useful when trying to probe areas of our universe that are surrounded by clouds of gas and dust. Because of infrared's longer wavelength, it can pass right through these clouds and reveal details invisible by observing other types of radiation. Especially interesting are areas were stars and planets are forming and the cores of galaxies where it is believed huge black holes might reside.
The image on the left shows an optical view of a star forming region. The same area is shown
on the right in infrared radiation. Notice how the infrared observations penetrate the obscuring
cloud to reveal many new details.
How will Gemini "see" infrared better?
Astronomers use special sensors to detect infrared radiation from space, but it's not easy. Because heat is given off by many objects (including the telescope and cameras themselves), everything must be carefully designed, and/or cooled to very cold temperatures.
Gemini has been designed to perform especially well when observing infrared radiation. This includes selecting the locations for the telescopes. Both scopes are located on high mountains where the air is very dry. Since atmospheric water vapor absorbs, or "soaks-up", infrared radiation, this was a very important consideration when selecting the sites for the Gemini telescopes. Gemini will also use special Silver coatings on its mirrors to reflect significantly more infrared radiation than the metals (usually aluminum) used on most other telescope mirrors.
Weird Infrared Signal Emanates Across Space, But What Created It?
Space is filled with bizarre signals that we scramble to put meaning to — and now, researchers have detected yet another mysterious signal. This one emanated from near a neutron star, and for the first time, it's infrared.
So, what's nearby that could have created the weird signal? Scientists have a few ideas.
When a star reaches the end of its life, it typically undergoes a supernova explosion— the star collapses, and if it has enough mass, it will form a black hole. But if the star isn't massive enough, it will form a neutron star. [Supernova Photos: Great Images of Star Explosions]
Neutrons stars are very dense and, as their name suggests, are made up mostly of closely packed neutrons. Neutron stars can also be called "pulsars" if they are highly magnetized and rotate rapidly enough to emit electromagnetic waves, according to Space.com.
Typically, neutron stars emit radio waves or higher-energy waves such as X-rays, according a statement released by NASA yesterday (Sept. 17). But an international group of researchers from Penn State, the University of Arizona and Sabanci University in Turkey observed something interesting in NASA's Hubble Space Telescope data: a long signal of infrared light emitted near a neutron star, the researchers reported yesterday in The Astrophysical Journal.
This signal, they found, was about 800 light-years away and was "extended," meaning it was spread across a large stretch of space, unlike typical "point" signals from neutron stars that emit X-rays. Specifically, the signal stretched across 200 astronomical units (AU) of space, or 2.5 times the orbit of Pluto around the sun, according to a statement from Penn State. (One AU is the average distance from Earth to the sun — about 93 million miles, or 150 million kilometers.)
Such extended signals have been observed before, but never in the infrared, lead author Bettina Posselt, an associate research professor of astronomy and astrophysics at Penn State, told Live Science.
Based on previous data, the amount of infrared radiation is much more than the neutron star should be emitting, Posselt said. So "all of the emission in infrared we see is likely not coming from the neutron star itself," Posselt said. "There's something more."
The neutron star in question, RX J0806.4-4123, is one of the nearby X-ray pulsars collectively known as the Magnificent Seven. They are bizarre characters: They rotate much more slowly than typical neutron stars (it takes 11 seconds for one rotation of RX J0806.4-4123, whereas typical ones rotate in a fraction of a second), and they're much hotter than they should be based on when they formed.
In their study, the researchers proposed two possibilities for what could have snuggled up near RX J0806.4-4123 and emitted these mysterious signals: a disk of dust that surrounds the pulsar, or a "pulsar wind nebula."
A "fallback disk" — that could stretch 18 billion miles across — could have formed from the remnants of a resident star following a supernova explosion, Posselt said. Such disks that "have been long searched for, but not found" would most likely be made up mainly of dust particles, she added.
The inner part of such a disk would likely have enough energy to produce infrared light, Posselt said. This could also help explain why RX J0806.4-4123 is so hot and spins so slowly. "The disks in the past could have provided some extra heating," and also slowed down its rotation, Posselt said.
The second explanation is that perhaps the infrared signal is coming from a nearby pulsar wind nebula.
A pulsar wind can form when electrons from a neutron star are accelerated in an electric field produced by the neutron star's fast rotation and strong magnetic field, according to the NASA statement. As the neutron star moves through space, typically faster than the speed of sound, it crashes into the interstellar medium — those tiny bits of gas and dust that reside between large celestial objects. The interaction between the interstellar medium and the pulsar wind can produce the so-called pulsar wind nebula, which could give off infrared radiation, Posselt said.
Pulsar wind nebulas are typically seen emitting X-rays, so a pulsar wind nebula that radiates only in the infrared is "definitely interesting," Posselt said.
So why is it so important to see in infrared?
Many of the things scientists want to observe in space are far too cold to radiate at optical or shorter wavelengths, but radiate strongly in infrared, for example, the cold atoms and molecules that drift in interstellar space. We need to study these raw materials to understand how stars form and evolve.
“By observing in the infrared we can study how things get formed, the very early steps, because formation processes very often happen in cool and dusty places,” explains Göran Pilbratt, ESA’s Herschel Project Scientist.
In our own Solar System, cold objects such as comets and asteroids reveal most of their characteristics to us in infrared light.
Other things of great interest to astronomy are hidden within or behind vast clouds of gas and dust. These clouds hide stars and planets in early stages of formation and the powerful cores of active galaxies.
Our view is blocked because the dust grains are very effective at scattering or absorbing visible light. Longer infrared wavelengths can get through the dust.
The future is extremely bright for infrared astronomy and, in the next decade, you will hear a lot about ESA discoveries in infrared astronomy!
Can stars be observed from space by x-rays, near infrared and radio wavelengths? - Astronomy
Context. The compact radio and near-infrared (NIR) source Sagittarius A* (Sgr A*) associated with the supermassive black hole in the Galactic center was observed at 7 mm in the context of a NIR triggered global Very Long Baseline Array (VLBA) campaign.
Aims: Sgr A* shows variable flux densities ranging from radio through X-rays. These variations sometimes appear in spontaneous outbursts that are referred to as flares. Multi-frequency observations of Sgr A* provide access to easily observable parameters that can test the currently accepted models that try to explain these intensity outbursts.
Methods: On May 16-18, 2012 Sgr A* has been observed with the VLBA at 7 mm (43 GHz) for 6 h each day during a global multi-wavelength campaign. These observations were triggered by a NIR flare observed at the Very Large Telescope (VLT). Accurate flux densities and source morphologies were acquired.
Results: The total 7 mm flux of Sgr A* shows only minor variations during its quiescent states on a daily basis of 0.06 Jy. An observed NIR flare on May 17 was followed
4.5 h later by an increase in flux density of 0.22 Jy at 43 GHz. This agrees well with the expected time delay of events that are casually connected by adiabatic expansion. Shortly before the peak of the radio flare, Sgr A* developed a secondary radio off-core feature at 1.5 mas toward the southeast. Even though the closure phases are too noisy to place actual constraints on this feature, a component at this scale together with a time delay of 4.5 ± 0.5 h between the NIR and radio flare provide evidence for an adiabatically expanding jet feature.
Why the infrared?
A few decades ago, astronomers realised that their view of the cosmos was, at best, only partial. It was not just a matter of seeing farther out, but also of using different eyes, eyes able to see other kinds of light or radiation.
For natural reasons, the sky was first studied in visible wavelengths, but with sophisticated technology, radiation from other parts of the electromagnetic spectrum have also come into play, initially in the radio, later at high energies such as X- and gamma-rays, and finally sensitive infrared observations have become possible. Telescopes sensitive to different wavelengths observe different facets of the Universe.
Infrared light was discovered about 200 years ago by the German-born British astronomer William Herschel.
About one half of the starlight produced and emitted throughout the history of the Universe has been absorbed and re-emitted as infrared light.
About one half of the energy produced and emitted throughout the history of the Universe has been absorbed and re-emitted as infrared light.
Different wavelengths of light reveal different natural phenomena, and the infrared has an important story to tell. One of the advantages of observing in the near-infrared is that dust is transparent to it. This is why an optical telescope would be unable to see a star enshrouded in dust, whereas one working in the near-infrared would be able to detect its emission. As one proceeds further into the far-infrared the emission from the dust itself becomes observable.
Relatively cold objects invisible to optical telescopes become visible in the infrared. Interstellar gas, planets and dust discs around other stars, asteroids, brown dwarfs (failed stars) and stars being born are all examples of objects that are too cold to shine in visible wavelengths but become conspicuous when viewed in the infrared. Direct infrared emission from cold dust is feeble, and Herschel's sensitivity will play a key role in its observation.
But why go into space to do this? For two very simple and important reasons: Earth's atmosphere blocks most infrared wavelengths, and in addition it also produces its own infrared radiation, overwhelming the celestial sources.