Category: star

Night sky just after sunset on March 24, 2012 …

Night sky just after sunset on March 24, 2012 with crescent moon and backlight, Jupiter, Venus and the Pleiades.



Spiral Galaxy 

Spiral Galaxy 

image credit: NASA/ESA, Hubble, Judy Schmidt, Robert Gendler @twitter

Images captured by NASA’s Spitzer Space …

Images captured by NASA’s Spitzer Space Telescope. (Some images include data from other telescopes)

The Spitzer Space Telescope is the final mission in NASA’s Great Observatories Program – a family of four space-based observatories, each observing the Universe in a different kind of light. The other missions in the program include the visible-light Hubble Space Telescope (HST), Compton Gamma-Ray Observatory (CGRO), and the Chandra X-Ray Observatory (CXO).

The Cryogenic Telescope Assembly, which contains the a 85 centimeter telescope and Spitzer’s three scientific instruments

The Spacecraft, which controls the telescope, provides power to the instruments, handles the scientific data and communicates with Earth

It may seem like a contradiction, but NASA’s Spitzer Space Telescope must be simultaneously warm and cold to function properly. Everything in the Cryogenic Telescope Assembly must be cooled to only a few degrees above absolute zero (-459 degrees Fahrenheit, or -273 degrees Celsius). This is achieved with an onboard tank of liquid helium, or cryogen.  Meanwhile, electronic equipment in The Spacecraft portion needs to operate near room temperature.

Spitzer’s highly sensitive instruments allow scientists to peer into cosmic regions that are hidden from optical telescopes, including dusty stellar nurseries, the centers of galaxies, and newly forming planetary systems. Spitzer’s infrared eyes also allows astronomers see cooler objects in space, like failed stars (brown dwarfs), extrasolar planets, giant molecular clouds, and organic molecules that may hold the secret to life on other planets.

Spitzer was originally built to last for a minimum of 2.5 years, but it lasted in the cold phase for over 5.5 years. On May 15, 2009 the coolant was finally depleted and the Spitzer “warm mission” began.  Operating with 2 channels from one of its instruments called IRAC, Spitzer can continue to operate until late in this decade. Check out: Fast Facts and Current Status.

Credit NASA | images: NASA/Spitzer

Galaxies: Types and morphology

A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. Galaxies range in size from dwarfs with just a few hundred million (108) stars to giants with one hundred trillion (1014) stars, each orbiting its galaxy’s center of mass.


Galaxies come in three main types: ellipticals, spirals, and irregulars. A slightly more extensive description of galaxy types based on their appearance is given by the Hubble sequence. 


Since the Hubble sequence is entirely based upon visual morphological type (shape), it may miss certain important characteristics of galaxies such as star formation rate in starburst galaxies and activity in the cores of active galaxies.



The Hubble classification system rates elliptical galaxies on the basis of their ellipticity, ranging from E0, being nearly spherical, up to E7, which is highly elongated. These galaxies have an ellipsoidal profile, giving them an elliptical appearance regardless of the viewing angle. Their appearance shows little structure and they typically have relatively little interstellar matter. Consequently, these galaxies also have a low portion of open clusters and a reduced rate of new star formation. Instead they are dominated by generally older, more evolved stars that are orbiting the common center of gravity in random directions.



Spiral galaxies resemble spiraling pinwheels. Though the stars and other visible material contained in such a galaxy lie mostly on a plane, the majority of mass in spiral galaxies exists in a roughly spherical halo of dark matter that extends beyond the visible component, as demonstrated by the universal rotation curve concept.

Spiral galaxies consist of a rotating disk of stars and interstellar medium, along with a central bulge of generally older stars. Extending outward from the bulge are relatively bright arms. In the Hubble classification scheme, spiral galaxies are listed as type S, followed by a letter (a, b, or c) that indicates the degree of tightness of the spiral arms and the size of the central bulge.

Barred spiral galaxy


A majority of spiral galaxies, including our own Milky Way galaxy, have a linear, bar-shaped band of stars that extends outward to either side of the core, then merges into the spiral arm structure. In the Hubble classification scheme, these are designated by an SB, followed by a lower-case letter (a, b or c) that indicates the form of the spiral arms (in the same manner as the categorization of normal spiral galaxies). 

Ring galaxy


A ring galaxy is a galaxy with a circle-like appearance. Hoag’s Object, discovered by Art Hoag in 1950, is an example of a ring galaxy. The ring contains many massive, relatively young blue stars, which are extremely bright. The central region contains relatively little luminous matter. Some astronomers believe that ring galaxies are formed when a smaller galaxy passes through the center of a larger galaxy. Because most of a galaxy consists of empty space, this “collision” rarely results in any actual collisions between stars.

Lenticular galaxy


A lenticular galaxy (denoted S0) is a type of galaxy intermediate between an elliptical (denoted E) and a spiral galaxy in galaxy morphological classification schemes. They contain large-scale discs but they do not have large-scale spiral arms. Lenticular galaxies are disc galaxies that have used up or lost most of their interstellar matter and therefore have very little ongoing star formation. They may, however, retain significant dust in their disks.

Irregular galaxy


An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy. Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arm structure.

Dwarf galaxy


Despite the prominence of large elliptical and spiral galaxies, most galaxies in the Universe are dwarf galaxies. These galaxies are relatively small when compared with other galactic formations, being about one hundredth the size of the Milky Way, containing only a few billion stars. Ultra-compact dwarf galaxies have recently been discovered that are only 100 parsecs across.



Interactions between galaxies are relatively frequent, and they can play an important role in galactic evolution. Near misses between galaxies result in warping distortions due to tidal interactions, and may cause some exchange of gas and dust. Collisions occur when two galaxies pass directly through each other and have sufficient relative momentum not to merge.



Stars are created within galaxies from a reserve of cold gas that forms into giant molecular clouds. Some galaxies have been observed to form stars at an exceptional rate, which is known as a starburst. If they continue to do so, then they would consume their reserve of gas in a time span less than the lifespan of the galaxy. Hence starburst activity usually lasts for only about ten million years, a relatively brief period in the history of a galaxy.

Active galaxy

A portion of the observable galaxies are classified as active galaxies if the galaxy contains an active galactic nucleus (AGN). A significant portion of the total energy output from the galaxy is emitted by the active galactic nucleus, instead of the stars, dust and interstellar medium of the galaxy.


The standard model for an active galactic nucleus is based upon an accretion disc that forms around a supermassive black hole (SMBH) at the core region of the galaxy. The radiation from an active galactic nucleus results from the gravitational energy of matter as it falls toward the black hole from the disc. In about 10% of these galaxies, a diametrically opposed pair of energetic jets ejects particles from the galaxy core at velocities close to the speed of light. The mechanism for producing these jets is not well understood.


The main known types are: Seyfert galaxies, quasars, Blazars, LINERS and Radio galaxy.

  • source
  • images: NASA/ESA, Hubble (via wikipedia)

Summary: The evolution of our universe accordi…

The Big Bang theory is the prevailing cosmological model for the universe from the earliest known periods through its subsequent large-scale evolution. The model describes how the universe expanded from a very high-density and high-temperature state, and offers a comprehensive explanation for a broad range of phenomena, including the abundance of light elements, the cosmic microwave background (CMB), large scale structure and Hubble’s law. If the known laws of physics are extrapolated to the highest density regime, the result is a singularity which is typically associated with the Big Bang. Physicists are undecided whether this means the universe began from a singularity, or that current knowledge is insufficient to describe the universe at that time. Detailed measurements of the expansion rate of the universe place the Big Bang at around 13.8 billion years ago, which is thus considered the age of the universe. After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later simple atoms. Giant clouds of these primordial elements later coalesced through gravity in halos of dark matter, eventually forming the stars and galaxies visible today.

1° Planck epoch <10−43 seconds


0 seconds: Planck Epoch begins: earliest meaningful time. The Big Bang occurs in which ordinary space and time develop out of a primeval state (possibly a virtual particle or false vacuum) described by a quantum theory of gravity or “Theory of Everything”. All matter and energy of the entire visible universe is contained in an unimaginably hot, dense point (gravitational singularity), a billionth the size of a nuclear particle. This state has been described as a particle desert. Other than a few scant details, conjecture dominates discussion about the earliest moments of the universe’s history since no effective means of testing this far back in space-time is presently available. WIMPS (weakly interacting massive particles) or dark matter and dark energy may have appeared and been the catalyst for the expansion of the singularity. The infant universe cools as it begins expanding outward. It is almost completely smooth, with quantum variations beginning to cause slight variations in density.

2° Grand unification epoch

10−43 seconds


Grand unification epoch begins: While still at an infinitesimal size, the universe cools down to 1032 kelvin. Gravity separates and begins operating on the universe—the remaining fundamental forces stabilize into the electronuclear force, also known as the Grand Unified Force or Grand Unified Theory (GUT), mediated by (the hypothetical) X and Y bosons which allow early matter at this stage to fluctuate between baryon and lepton states.

3° Electroweak epoch

10−36 seconds: Electroweak epoch begins: The Universe cools down to 1028 kelvin. As a result, the Strong Nuclear Force becomes distinct from the Electroweak Force perhaps fuelling the inflation of the universe. A wide array of exotic elementary particles result from decay of X and Y bosons which include W and Z bosons and Higgs bosons.


10−33 seconds: Space is subjected to inflation, expanding by a factor of the order of 1026 over a time of the order of 10−33 to 10−32 seconds. The universe is supercooled from about 1027 down to 1022 kelvin.


10−32 seconds: Cosmic inflation ends. The familiar elementary particles now form as a soup of hot ionized gas called quark-gluon plasma; hypothetical components of Cold dark matter (such as axions) would also have formed at this time.

4° Quarks epoch

10−12 seconds: Electroweak phase transition: the four fundamental interactions familiar from the modern universe now operate as distinct forces. The Weak nuclear force is now a short-range force as it separates from Electromagnetic force, so matter particles can acquire mass and interact with the Higgs Field. The temperature is still too high for quarks to coalesce into hadrons, and the quark-gluon plasma persists (Quark epoch). The universe cools to 1015 kelvin.

10−11 seconds: Baryogenesis may have taken place with matter gaining the upper hand over anti-matter as baryon to antibaryon constituencies are established.

Hadron epoch  10−6 seconds


Hadron epoch begins: As the universe cools to about 1010 kelvin, a quark-hadron transition takes place in which quarks bind to form more complex particles—hadrons. This quark confinement includes the formation of protons and neutrons (nucleons), the building blocks of atomic nuclei.

Lepton Epoch 1 second

Lepton epoch begins: The universe cools to 109 kelvin. At this temperature, the hadrons and antihadrons annihilate each other, leaving behind leptons and antileptons – possible disappearance of antiquarks. Gravity governs the expansion of the universe: neutrinos decouple from matter creating a cosmic neutrino background.

7° Photon epoch (Matter era )


10 seconds: Photon epoch begins: Most of the leptons and antileptons annihilate each other. As electrons and positrons annihilate, a small number of unmatched electrons are left over – disappearance of the positrons.

10 seconds: Universe dominated by photons of radiation – ordinary matter particles are coupled to light and radiation while dark matter particles start building non-linear structures as dark matter halos. Because charged electrons and protons hinder the emission of light, the universe becomes a super-hot glowing fog.

3 minutes: Primordial nucleosynthesis: nuclear fusion begins as lithium and heavy hydrogen (deuterium) and helium nuclei form from protons and neutrons.

20 minutes: Nuclear fusion ceases: normal matter consists of 75% hydrogen and 25% helium – free electrons begin scattering light.

70,000 years: Matter domination in Universe: onset of gravitational collapse as the Jeans length at which the smallest structure can form begins to fall.

8° Cosmic Dark Age

370,000 years

The “Dark Ages” is the period between decoupling, when the universe first becomes transparent, until the formation of the first stars. Recombination: 


electrons combine with nuclei to form atoms, mostly hydrogen and helium. Distributions of hydrogen and helium at this time remains constant as the electron-baryon plasma thins. The temperature falls to 3000 kelvin.


Ordinary matter particles decouple from radiation. The photons present at the time of decoupling are the same photons that we see in the cosmic microwave background (CMB) radiation.

10 million years: With a trace of heavy elements in the Universe, the chemistry that later sparked life begins operating.

100 million years: Gravitational collapse: ordinary matter particles fall into the structures created by dark matter. Reionization begins: smaller (stars) and larger non-linear structures (quasars) begin to take shape – their ultraviolet light ionizes remaining neutral gas.


200–300 million years: First stars begin to shine: Because many are Population III stars (some Population II stars are accounted for at this time) they are much bigger and hotter and their life-cycle is fairly short. Unlike later generations of stars, these stars are metal free. As reionization intensifies, photons of light scatter off free protons and electrons – Universe becomes opaque again.


600 million years: Renaissance of the Universe—end of the Dark Ages as visible light begins dominating throughout. Possible formation of the Milky Way Galaxy: although age of the Methusaleh star suggests a much older date of origin, it is highly likely that HD 140283 may have come into our galaxy via a later galaxy merger. Oldest confirmed star in Milky Way Galaxy, HE 1523-0901.


700 million years: Galaxies form. Smaller galaxies begin merging to form larger ones. Galaxy classes may have also begun forming at this time including Blazars, Seyfert galaxies, radio galaxies, normal galaxies (elliptical, Spiral galaxies, barred spiral) and dwarf galaxies.


7.8 billion years: Acceleration: dark-energy dominated era begins, following the matter-dominated era in during which cosmic expansion was slowing down

Formation of the solar system

9.2 billion years: Primal supernova, possibly triggers the formation of the Solar System.

9.2318 billion years: Sun forms – Planetary nebula begins accretion of planets.


9.23283 billion years: Four Jovian planets (Jupiter, Saturn, Uranus, Neptune ) evolve around the sun.

9.257 billion years: Solar System of Eight planets, four terrestrial (Mercury (planet), Venus, Earth, Mars) evolve around the sun.

Twinkling stars are far more desirable to poet…

Twinkling stars are far more desirable to poets and romantics than to astronomers. Even in the near-pristine seeing conditions over Chile, home to ESO’s fleet of world-class telescopes, turbulence in Earth’s atmosphere causes stars to twinkle, blurring our view of the night sky.

These four laser beams are specially designed to combat this turbulence. The intense orange beams dominating this image originate from the 4 Laser Guide Star Facility, a state-of-the-art component of the Adaptive Optics Facility of ESO’s Very Large Telescope (VLT). Each beam is some 4000 times more powerful than a standard laser pointer! Each creates an artificial guide star by exciting sodium atoms high in the Earth’s upper atmosphere and causing them to glow.

Creating artificial guide stars allows astronomers to measure and correct for atmospheric distortion, by adjusting and calibrating the settings of their observing equipment to be as accurate as possible for that particular area of sky. This gives the VLT a crystal-clear view of the cosmos, so it can capture the wonders of the Universe in stunning detail.

The first image was made using a drone flying over the VLT by the ESO Photographic Ambassador, Gerhard Hüdepohl.


Image credit:

ESO/G. Hüdepohl, Babak Tafreshi, Mark McCaughrean

The globular cluster NGC 104 

The globular cluster NGC 104 

Credit: ESO  twitter: @astronomy_blog | instagram: @astronomy_blog

Star-forming region RCW 108 in Ara. RCW 108…

Star-forming region RCW 108 in Ara.

RCW 108 is a molecular cloud that is in the process of being destroyed by intense ultraviolet radiation from heavy and hot stars in the nearby stellar cluster NGC 6193, seen to the left in the photo. 

Credit: ESO

This image taken on Oct. 19, 2013, shows a f…

This image taken on Oct. 19, 2013, shows a filament on the sun – a giant ribbon of relatively cool solar material threading through the sun’s atmosphere, the corona. The individual threads that make up the filament are clearly discernible in this photo. This image was captured by the Solar Optical Telescope onboard JAXA/NASA’s Hinode solar observatory. Researchers studied this filament to learn more about material gets heated in the corona.

Credits: JAXA/NASA/Hinode

Located in the Southern Hemisphere, NGC 3324…

Located in the Southern Hemisphere, NGC 3324 is at the northwest corner of the Carina Nebula (NGC 3372), home of the Keyhole Nebula and the active, outbursting star Eta Carinae. The entire Carina Nebula complex is located at a distance of roughly 7,200 light-years, and lies in the constellation Carina.

Image credit: NASA/ESA/Hubble