Images of Galaxies and Stars outside the Visible Light Range Part-2 - Remote Sensing Application - Completely Remote Sensing, GPS, and GPS Tutorial
Images of Galaxies and Stars outside the Visible Light Range Part-2

In December of 1999, the European Space Agency launched an even more powerful X-ray telescope known as XMM-Newton (XMM stands for X-ray Multi-Mirror). Here are two colorized images, the first showing the variations in X-ray intensities in several of the Hickson group of stars and the second showing details of a supernova explosion in the nearby Large Magellanic Cloud:

XMM image of Hickson stars. XMM image of part of a supernova in the Large Magellanic Cloud

XMM-Newton has demonstrated that large X-ray energy bursts also associate with the starbursts that mark development of young stars. Here is an image of NGC253, some 8 million light years from Earth; the inset on the left is a closer look at its center.

X-ray image and intensity contours in the starburst cluster within NGC253, as seen by XMM-Newton.

A notable discovery made by XMM-Newton is a huge (109 solar masses) concentration of fast-moving (1000 km/sec) gas, shown in this image:

Entropy map of the 'mega-comet' in Abell 3266.

This mass of gas has been likened to a "mega-comet" (but it is not a true comet in the Solar System sense) some 5 million light years in length. The gas appears red to yellow, representing the mapping of data into entropy values. The feature is within the galaxy cluster Abell 3266. Its discoverers believe it to be held together by Dark Matter.

XMM-Newton has taken a series of images over a period of days that can be sequenced to give a movie-like effect of the expansion and dissipation of materials during a burst. We will cite the Internet connection on which this dynamic rendition can be accessed - with the proviso that it may no longer be active. So, click on starburst to see if the "show goes on".

Still on the drawing boards (not fully funded) is the Constellation-X Observatory that will be the most sophisticated X-ray satellite yet; launch will be in 2017 or later.

Satellites began to examine the UV region of the sky with the OAO series (OAO-3 was named Copernicus) in the late 1960's. Copernicus produced maps of bright UV stars such as this:

Some of the bright stars imaged in the UV by Copernicus (launched in 1972)

The ultraviolet (UV) region of the spectrum, from 70-2000 (0.007 - 0.2 µm) (Far) to 2000-4000 Angstroms (0.2 - 0.4 µm) (Near), has provided interesting images of stellar bodies, including the Sun. It also contains many diagnostic spectral lines helpful in determining elemental composition. In the 1970s, the Soviet space program installed UV Observatories, named Orion 1 and Orion 2, on a Salyut and Soyuz spacecraft respectively.

This next image shows the Earth as imaged by EUVE (Extreme UltraViolet Explorer, a free flying observatory launched in 1992 and operating until February, 2001; imaging from 70 to 760 Angstroms). It shows excited Helium (yellow) and Hydrogen (orange-red) in an auroral field extending well beyond the solid Earth.

UV image of Earth, taken from the EUVE satellite

Looking outward into space, the EUVE provided this image of the Vela Supernova:

UV image of excited gaseous remnants of the Vela Supernova.

One of the first UV telescopes is the IUE (International Ultraviolet Explorer) launched jointly by ESA and NASA in 1978; it operated into 1996. This is a UV image of the galactic source NGC1680:

Color-coded image of NGC1680 acquired by the IUE.

The Ultraviolet Imaging Telescope (UIT) was flown as part of Astro-1 and Astro-2 lab packages on Shuttle STS-35 and STS-67 in the mid-1990s. The telescope covers the UV range between 1200 and 3200 Angstroms. It is particularly adept at recognizing hot, young stars which give out strong UV radiation. The difference in appearance between visible and ultraviolet images is pronounced in this UIT view of the galaxy M94:

UIT images of M94; visible light (above) shows the dominance of old, red stars at this wavelength internval; the UV image (below) reveals a ring of hot, young, blue stars.

This next image shows three galaxies in UV (top) and Visible (bottom); note the structure of the spiral arms as brought out by molecular Hydrogen excitation.

UV and Visible images of three galaxies; the top group was obtained by the UIT.

In the UIT image below, the globular cluster Omega Centauri in visible light appears to consist of mainly red to orange stars, typical of older stellar bodies. But, the UV on the right shows that there are also many younger, hotter stars.

UIT image (right) of the Omega Centauri star cluster.

Launched on June 24, 1999, FUSE (Far Ultraviolet Spectroscopic Explorer) gathers spectra in the interval 910 - 1180 Angstroms. The program is run out of Johns Hopkins University, with NASA, French, and Canadian partners.

Excitation of molecular and elemental species in a star's atmosphere or a galaxy en masse in this interval provides valuable information about stellar processes. Here is a typical spectral plot obtained by FUSE from observing a galaxy.

UV spectral curve for NGC 4151, plotted from data received by FUSE.

Observations through the FUSE telescope can be converted to images, such as this:

Image of bright stars and gases in the Ara Galaxy, made by FUSE.

FUSE's primary goal has been to trace the history of the early Universe by monitoring the distribution of Hydrogen (H), Deuterium (D), and Helium (He) in the intergalactic medium. Deuterium was detected in this FUSE UV image of star AE Aurigae, which in visible light is shrouded by dust:

FUSE image of AE Aurigae.

Preliminary results from FUSE indicate that Helium, formed in the first minute of the Big Bang, and then dispersed during the expansion, will prove a sensitive indicator of the inhomogenieties in the expanding Universe following the initial explosion. This is a generalized diagram of the ratio of D to H since the Big Bang, as Deuterium is converted to He through H fusion (thus, decreasing the ratio).

Generalized plot of the changing ratio of D/H over cosmic time.

JPL has developed GALEX (Galaxy Evolution Explorer), which was launched on April 28, 2003. Designed to gather imagery in the far and near ultraviolet (FUV and NUV), it will concentrate on monitoring distant galaxies and stars (out to at least 10 billion l.y.) to determine the conditions under which they had formed in the early years of the Universe. This image of Galaxy M101 was made by combining the FUV (blue) and NUV (green) images:

GALEX image of M101.

Here are a trio of images of Galaxy M51, one in the UV (GALEX), the middle from an optical telescope, and the one on the right in the Near-IR (2Mass project)

Galaxy M51, imaged by GALEX (UV), optical telescope (Vis), and a 2Mass telescope (Near-IR).

A final look at a galaxy imaged by GALEX entirely in the UV: NGC 1232 is shown here as a partial false color composite made from two UV bands:

UV image of NGC1232

Thus, the UV is proving to be an optimum segment of the EM spectrum to study conditions in the so-called empty space which actually contains hot interstellar gas. CHIPS (Cosmic Hot Interstellar Plasma Spectrometer) is an astronomy satellite (called CHIPSat) launched on January 12, 2003. It conducts an all-sky spectroscopic survey of the diffuse background at wavelengths from 90 to 260 � with a peak resolution of about 0.5 eV. CHIPS data is helping scientists determine the electron temperature, ionization conditions, and cooling mechanisms of the million-degree plasma believed to fill the local interstellar bubble. The majority of the luminosity from diffuse million-degree plasma is expected to emerge in the poorly-explored CHIPS band, making CHIPS data of relevance in a wide variety of Galactic and extragalactic astrophysical environments. Thus, it has measured the diffuse extreme ultraviolet glow that will better define the properties and physical processes associated with the interstellar medium. A review by Univ. of Calif-Berkeley scientists of the mission's purpose and some results is available at this UC-Berkeley site. Using CHIPS data, in part, this map of the local bubble around the Sun extending to nearby stars has been published:

Map of the hot Hydrogen gas in the local interstellar bubble that includes the Sun.

In 2004. NASA, along with several cooperating Universities and organizations, launched SWIFT, a telescope observatory satellite whose prime mission is to search for Gamma Ray Bursts and then examine their sites in UV and Visible light. SWIFT carries a gamma-ray detector, an X-ray detector, and a detector whose operational range includes parts of the UV and Visible. Below is the first image, of the Pinwheel Galaxy, made by this third instrument:

The Pinwheel Galaxy (M101), as imaged by the UVOT instrument onboard SWIFT.

SWIFT made this time lapse set of images of a short-lived burst from a neutron star, SGB J1550-5418, in which X-rays have excited dust surrounding it, so that a dispersed cloud of material is evident as an expanding ring:

A sequence of views of an expanding ring around a neutron star.

This next pair of dual images shows one of the typical gamma-ray burst sequences sought by SWIFT. In the top image, the left view shows SN 2007uy (labelled) and a star above it that will become SN 2008D, seen on the left view of the lower image. This burst is evident in the visible image (right; lower) near the "top" of galaxy 2770.

SWIFT images showing the Supernova 2007uy and the beginning of the gamma-ray burst that would become SN2008D.
SN2008D has now developed.

The UV is particularly suited to spotting active star formation in galaxies. Andromeda has numerous super-bright regions of young stars, as seen by Swift.

Andromeda seen in UV.

The UV carries into the Visible spectral range. Just beyond the Visible is the Infrared, extending from about 1 to 1000 µm. Much of the interval coincides with the thermal IR which you studied in Section 9. Hot stars are strong emitters in the IR and can be studied both as images and from their spectra. Other astronomical features amenable to IR observations include properties of accretionary disks and interstellar clouds, the structure of the H II type stars (those in an early stage of development that contain significant ionized Hydrogen in the inner part of the Hydrogen gas cloud that is the source of their nuclear fuel), and the dynamics of the Milky Way.

Viewing galaxies and regions of heavy dust densities in the Infrared has a distinct benefit compared with seeing the same features in the Visible. This image pair vets this statement (read its caption):

A part of the Milky Way seen in visible (left) and infrared (right) light, showing how obscuration by dust in the visible is largely nullified when the same region is viewed in the infrared.

Small dark interstellar dust that obscures stars in the Visible are called Bok Globules (discovered by a Dutch astronomer of that name). They represent nebular gas and dust nearing the protostar phase (see page 20-2); such molecular Hydrogen clouds are very cold (-263°C) and generally because of their small size (about a parsec) produce only one to several stars. These globules (some of which can be nearly spherical) stand out best in images that extend into the Near IR. These two photos (acquired by ESA's New Technology Telescope) show details of a Bok Globule in Barnard 68. The left image is made from three bands in the visible; the right image consists of bands at 1.25 µm = Blue; 1.65 µm = green; and 2.16 µm = red, which renders the cloud now partially transparent so that stars behind it become visible.

Visible HST image of the Bok Cloud Stars appear within/behind the Bok Globule cloud when viewed in the NIR.

An entire galaxy (NGC2024) that is still largely shrouded by dust looks much like a visible image in this version made by the NICMOS camera on HST. The color composite consists of Blue = J band (1.6 µm); Red = K band (2.2 µm); and Green = J and K combined.

NGC2024 in a color composite using IR bands in the NICMOS camera.

The Infrared region of the EM Spectrum has a treasuretrove of information. Hot stars are often shrouded in dust but some IR bands are "transparent" relative to that blocking material, allowing the stellar thermal source to shine through. One of the first infrared-dedicated satellites was IRAS (Infrared Astronomical Satellite) launched in January of 1983. Its sensors were tuned to the 12, 25, 60, and 100 µm IR wavelengths. Here it is at the dirt-free facility at Goddard Space Flight Center - at the time just a hundred meters from my office:

The IRAS spacecraft; the sunshield cowl is lined with gold foil on its inside.

During its lifetime, IRAS discovered more than 350,000 previously undetected IR objects in the sky. This color composite of the interstellar "cirrus" clouds made up of gas and dust grains in the Milky Way that occupy a wide field centered on the North Celestial Pole is constructed from Blue = 12; Green = 60; Red = 100 µm.

Interstellar gas-dust in the Milky Way, as imaged by IRAS

On a grander scale, look at this IRAS image of the now familiar neighbor, the Andromeda Galaxy, with color-codes indicating variations in thermal emission at 12 µm.

The Andromeda Galaxy

One of the finest IRAS images is this 25, 60, 100 µm color composite showing the nebular material around Lambda Ori:

The Lambda Ori region as seen by IRAS.

Other IR observatories have since been placed in space. ISO, the Infrared Space Observatory, was operated by ESA from November '95 until May '98. The instruments include an IR camera, a spectrometer, and a polarimeter. The spectral range was 2.5 to 240 µm. Here is a painting of the ISO:

The Infrared Space Observatory.

These ISO images of the familiar Andromeda galaxy are typical of this observatory's products.

Andromeda galaxy, as seen by ISO.

ISO can monitor the spectra of various celestial objects. This example shows the results for an interstellar cirrus-like nebula; CarbonII is a major constituent:

Image of a cirrus-like nebula, with its partial spectrum superimposed.

A IR wavelength plot of radiation received from NGC6543 shows peaks correlated with Argon, Neon, Hydrogen, and Sulphur which occurs in the dust and gas nebula associated with this, the Antennae galaxy.

Spectra for the Antennae Galaxy, obtained by ISO.

The star GL2591 is surrounded by a dense cloud. Spectra in the Short Wave IR interval sampled by IS0's spectrometer disclose water ice, carbon dioxide ice and silicate particles in the dust grains within the enclosing material.

SWIR Spectra from the dust sheath around Star GL2591.

On August 24, 2003 NASA launched a major new telescope - one of the Big Four of the Great Observatory series in its current astronomy programs - SIRTF (Space Infrared Telescope Facility). Following a contest to rename this powerful new sky-searcher, it is now called the Spitzer Space Telescope (SST), named after the pioneer astronomer Lyman Spitzer. SST is comparable in its capabilities to the HST and Chandra. The orbit is heliocentric and Earth-trailing. Its instruments operate in the infrared between 3 and 180 µm, which includes much of the thermal infrared spectral region. Its primary mission will be to peer through cosmic clouds and dust (usually, transparent in the infrared) to look back in time to see galaxies and stars in their earlier stages of development. A preview of the SST is given at a JPL lecture. Access this at von Karman lectures, entering Webcast into the Format box, and choosing the topic "The Space Infrared Telescope Facility", June 12, 2003, clicking on RealPlayer.

Here is a sketch of the SST in orbit:

First data were released on December 18 of 2003. This panel of four images is typical of first results:

Four SST images; see text below for identification.

The upper left panel shows the spiral galaxy M81 in a false color thermal infrared composite. Upper right is a Haro-Herbig star seen as a thermal object (in visible light it is masked by clouds). The lower left panel is a view of Comet Schwassmann-Wachman; the remaining panel shows the Dark Globule IC1396 (ordinarily indistinct in visible light).

This illustration enlarges the Dark Globule IC1396 and shows on the right this same image as sensed by two of the instruments on SST.

Three views of the Dark nebula in Globule IC1396l

As stated above, one powerful attribute of the SST is its ability to "see" through thick clouds of dust. A region within the Milky Way about 10000 l.y. away contains a great clot of dark dust in which almost no stars are visible. When viewed in the IR by SST, stars and glowing gas were revealed. Among these were some very large stars, demonstrating that stars up to 100 times more massive than the Sun are still forming in our galaxy and, by inference, probably throughout the Universe (thus big stars can be recent in time of formation, even though not long-lived).

Penetration of a thick dust cloud in the Milky Way, revealing in infrared light that hot gases and massive stars are still in their formative stages.

This ability to penetrate unresolved dust or close-spaced, very distant galaxies is making Spitzer a powerful tool for studying galaxies formed early in Universe history. The left image below shows what appears to be a uniform nebula imaged in the infrared from the ground by the United Kingdom's SCUBA instrument; nothing beyond is visible. When the SST looked at the same area, at different IR wavelengths, faint galaxies (arrows), very far away and hence seen now in their earlier stages, are now resolved (the bright orange feature is a nearby star in the line of sight.

A small segment of the distant sky in which a masking nebular mass has been penetrated by the Spitzer Space Telescope to reveal distant galaxies (two are indicated by arrows).

Source: http://rst.gsfc.nasa.gov/