Thursday, 26 January 2012

X-RAYS..........


X-Raysan illustration of the x-ray region of the electromagnetic spectrum from 100 eV to 200 KeV. Soft x-rays have lower energy than hard x-rays. The wavelength of x-rays is about the size the diameter of an atom.

X-RAYS AND ENERGY

X-rays have much higher energy and much shorter wavelengths than ultraviolet light, and scientists usually refer to x-rays in terms of their energy rather than their wavelength. This is partially because x-rays have very small wavelengths, between 0.03 and 3 nanometers, so small that some x-rays are no bigger than a single atom of many elements.
a series of 12 x-ray images showing the various level of activity on the Sun.
This mosaic of several Chandra X-ray Observatory images of the central region of our Milky Way galaxy reveals hundreds of white dwarf stars, neutron stars, and black holes. Separately, the Solar and Heliophysics Observatory (SOHO) captured these images of the Sun representing an entire solar cycle from 1996 through 2006. Credit: NASA/UMass/D.Wang et al. Sun images from SOHO – EIT Consortium: NASA/ESA

DISCOVERY OF X-RAYS

X-rays were first observed and documented in 1895 by German scientist Wilhelm Conrad Roentgen. He discovered that firing streams of x-rays through arms and hands created detailed images of the bones inside. When you get an x-ray taken, x-ray sensitive film is put on one side of your body, and x-rays are shot through you. Because bones are dense and absorb more x-rays than skin does, shadows of the bones are left on the x-ray film while the skin appears transparent.
An x-ray image of teeth
An x-ray image of teeth. Can you see the filling?
An X-ray photo of a one year old girl who swallowed a sewing pin
An X-ray photo of a one year old girl who swallowed a sewing pin. Can you find it?
Our Sun's radiation peaks in the visual range, but the Sun's corona is much hotter and radiates mostly x-rays. To study the corona, scientists use data collected by x-ray detectors on satellites in orbit around the Earth. Japan's Hinode spacecraft produced these x-ray images of the Sun that allow scientists to see and record the energy flows within the corona.
An x-ray image of the Sun showing detail of solar flares and sun spot activity that is not visible to our eyes.
Credit: Hinode JAXA/NASA/PPARC

TEMPERATURE AND COMPOSITION

The physical temperature of an object determines the wavelength of the radiation it emits. The hotter the object, the shorter the wavelength of peak emission. X-rays come from objects that are millions of degrees Celsius—such as pulsars, galactic supernovae remnants, and the accretion disk of black holes.
From space, x-ray telescopes collect photons from a given region of the sky. The photons are directed onto the detector where they are absorbed, and the energy, time, and direction of individual photons are recorded. Such measurements can provide clues about the composition, temperature, and density of distant celestial environments. Due to the high energy and penetrating nature of x-rays, x-rays would not be reflected if they hit the mirror head on (much the same way that bullets slam into a wall). X-ray telescopes focus x-rays onto a detector using grazing incidence mirrors (just as bullets ricochet when they hit a wall at a grazing angle).
NASA's Mars Exploration Rover, Spirit, used x-rays to detect the spectral signatures of zinc and nickel in Martian rocks. The Alpha Proton X-Ray Spectrometer (APXS) instrument uses two techniques, one to determine structure and another to determine composition. Both of these techniques work best for heavier elements such as metals.

SUPERNOVA

Since Earth's atmosphere blocks x-ray radiation, telescopes with x-ray detectors must be positioned above Earth's absorbing atmosphere. The supernova remnant Cassiopeia A (Cas A) was imaged by three of NASA's great observatories, and data from all three observatories were used to create the image shown below. Infrared data from the Spitzer Space Telescope are colored red, optical data from the Hubble Space Telescope are yellow, and x-ray data from the Chandra X-ray Observatory are green and blue.
The x-ray data reveal hot gases at about ten million degrees Celsius that were created when ejected material from the supernova smashed into surrounding gas and dust at speeds of about ten million miles per hour. By comparing infrared and x-ray images, astronomers are learning more about how relatively cool dust grains can coexist within the super-hot, x-ray producing gas.
A vibrant multi-colored cloud describes how supernova CAS-A looks in this x-ray image composite.
Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA/JPL-Caltech/Steward/O.Krause et al.

EARTH'S AURORA IN X-RAYS

Solar storms on the Sun eject clouds of energetic particles toward Earth. These high-energy particles can be swept up by Earth's magnetosphere, creating geomagnetic storms that sometimes result in an aurora. The energetic charged particles from the Sun that cause an aurora also energize electrons in the Earth's magnetosphere. These electrons move along the Earth's magnetic field and eventually strike the Earth's ionosphere, causing the x-ray emissions. These x-rays are not dangerous to people on the Earth because they are absorbed by lower parts of the Earth's atmosphere. Below is an image of an x-ray aurora by the Polar Ionospheric X-ray Imaging Experiment (PIXIE) instrument aboard the Polar satellite.
A view of the Earth's north pole with a color map of an aurora in x-ray. A large red area showing the most intensity is over northern Canada.
Credit: POLAR, PIXIE, NASA

Sunday, 22 January 2012

GAMMA RAYS

an illustration of the Gamma Ray region of the electromagnetic spectrum from 200 KeV to 200 MeV. These high energy waves have wavelengths about the size of the diameter of an atom's nucleus.

SOURCES OF GAMMA RAYS

detail of an all-sky color map of gamma ray sources in the night sky.  A large bright area of gamma ray sources from the Milky Way galaxy stretch across the center.
Brighter colors in the Cygus region indicate greater numbers of gamma rays detected by the Fermi gamma-ray space telescope. Credit: NASA/DOE/International LAT Team
Gamma rays have the smallest wavelengths and the most energy of any wave in the electromagnetic spectrum. They are produced by the hottest and most energetic objects in the universe, such as neutron stars and pulsars, supernova explosions, and regions around black holes. On Earth, gamma waves are generated by nuclear explosions, lightning, and the less dramatic activity of radioactive decay.

DETECTING GAMMA RAYS

Unlike optical light and x-rays, gamma rays cannot be captured and reflected by mirrors. Gamma-ray wavelengths are so short that they can pass through the space within the atoms of a detector. Gamma-ray detectors typically contain densely packed crystal blocks. As gamma rays pass through, they collide with electrons in the crystal. This process is called Compton scattering, wherein a gamma ray strikes an electron and loses energy, similar to what happens when a cue ball strikes an eight ball. These collisions create charged particles that can be detected by the sensor.
This diagram shows how a photon from incoming energy hits an electron at rest. The photon scatters and the electron recoils at the same angle in the opposite direction.

GAMMA RAY BURSTS

Gamma-ray bursts are the most energetic and luminous electromagnetic events since the Big Bang and can release more energy in 10 seconds than our Sun will emit in its entire 10-billion-year expected lifetime! Gamma-ray astronomy presents unique opportunities to explore these exotic objects. By exploring the universe at these high energies, scientists can search for new physics, testing theories and performing experiments that are not possible in Earth-bound laboratories.
If we could see gamma rays, the night sky would look strange and unfamiliar. The familiar view of constantly shining constellations would be replaced by ever-changing bursts of high-energy gamma radiation that last fractions of a second to minutes, popping like cosmic flashbulbs, momentarily dominating the gamma-ray sky and then fading.
NASA's Swift satellite recorded the gamma-ray blast caused by a black hole being born 12.8 billion light years away (below). This object is among the most distant objects ever detected.
An image of a gamma ray burst seen in gamma rays on left show s a bright burst of yellow, orange and red. The image on the right shows the same burst in visible and Ultraviolet as just a bright star in the center with some slight red and green coloring surrounding the star.
Credit: NASA/Swift/Stefan Immler, et al.

COMPOSITION OF PLANETS

Scientists can use gamma rays to determine the elements on other planets. The Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) Gamma-Ray Spectrometer (GRS) can measure gamma rays emitted by the nuclei of atoms on planet Mercury's surface that are struck by cosmic rays. When struck by cosmic rays, chemical elements in soils and rocks emit uniquely identifiable signatures of energy in the form of gamma rays. These data can help scientists look for geologically important elements such as hydrogen, magnesium, silicon, oxygen, iron, titanium, sodium, and calcium.
The gamma-ray spectrometer on NASA's Mars Odyssey Orbiter detects and maps these signatures, such as this map (below) showing hydrogen concentrations of Martian surface soils.
A color map of Mars showing the distribution of hydrogen by mapping the lower-limit of water mass fraction.
Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio

GAMMA RAY SKY

Gamma rays also stream from stars, supernovas, pulsars, and black hole accretion disks to wash our sky with gamma-ray light. These gamma-ray streams were imaged using NASA's Fermi gamma-ray space telescope to map out the Milky Way galaxy by creating a full 360-degree view of the galaxy from our perspective here on Earth.
an all-sky color map of gamma ray sources in the night sky.  A large bright area of gamma ray sources from the Milky Way galaxy stretch across the center.
A FULL-SPECTRUM IMAGE
The composite image below of the Cas A supernova remnant shows the full spectrum in one image. Gamma rays from Fermi are shown in magenta; x-rays from the Chandra Observatory are blue and green. The visible light data captured by the Hubble space telescope are displayed in yellow. Infrared data from the Spitzer space telescope are shown in red; and radio data from the Very Large Array are displayed in orange.
A multi-sensor composite image of a supernova. A multicolored image of gas and dust with an area highlighted showing GeV gamma-ray source.

Friday, 20 January 2012


Image of the Day Gallery

THE EAGLE NEBULA

The Eagle Nebula
THE EAGLE NEBULA



The Eagle Nebula

Combining almost opposite ends of the electromagnetic spectrum, this composite of the Herschel in far-infrared and XMM-Newton’s X-ray images shows how the hot young stars detected by the X-ray observations are sculpting and interacting with the surrounding ultra-cool gas and dust, which, at only a few degrees above absolute zero, is the critical material for star formation itself. Both wavelengths would be blocked by Earth’s atmosphere, so are critical to our understanding of the lifecycle of stars

Image Credit: ESA/Herschel/PACS/SPIRE/Hill, Motte, HOBYS Key Programme Consortium

Monday, 9 January 2012

chandra......exploring the invisible universe


Feature

Celestial Bauble Intrigues Astronomers
12.20.11
 
Composite image of pulsar SXP 1062

With the holiday season in full swing, a new image from an assembly of telescopes has revealed an unusual cosmic ornament. Data from NASA's Chandra X-ray Observatory and ESA's XMM-Newton have been combined to discover a young pulsar in the remains of a supernova located in the Small Magellanic Cloud, or SMC. This would be the first definite time a pulsar, a spinning, ultra-dense star, has been found in a supernova remnant in the SMC, a small satellite galaxy to the Milky Way.

In this composite image, X-rays from Chandra and XMM-Newton have been colored blue and optical data from the Cerro Tololo Inter-American Observatory in Chile are colored red and green. The pulsar, known as SXP 1062, is the bright white source located on the right-hand side of the image in the middle of the diffuse blue emission inside a red shell. The diffuse X-rays and optical shell are both evidence for a supernova remnant surrounding the pulsar. The optical data also displays spectacular formations of gas and dust in a star-forming region on the left side of the image. A comparison of the Chandra image with optical images shows that the pulsar has a hot, massive companion.

Astronomers are interested in SXP 1062 because the Chandra and XMM-Newton data show that it is rotating unusually slowly -- about once every 18 minutes. (In contrast, some pulsars are found to revolve multiple times per second, including most newly born pulsars.) This relatively leisurely pace of SXP 1062 makes it one of the slowest rotating X-ray pulsars in the SMC.

Two different teams of scientists have estimated that the supernova remnant around SXP 1062 is between 10,000 and 40,000 years old, as it appears in the image. This means that the pulsar is very young, from an astronomical perspective, since it was presumably formed in the same explosion that produced the supernova remnant. Therefore, assuming that it was born with rapid spin, it is a mystery why SXP 1062 has been able to slow down by so much, so quickly. Work has already begun on theoretical models to understand the evolution of this unusual object.

Credits: NASA/CXC/Univ. of Potsdam/L. Oskinova et al.

> Read more/access all images
 
 


Janet Anderson, 256-544-0034
Marshall Space Flight Center, Huntsville, Ala.
janet.l.anderson@nasa.gov

Megan Watzke 617-496-7998
Chandra X-ray Center, Cambridge, Mass.
m.watzke@cfa.harvard.edu