SPACE ANIMALS
Animal in space :
Male Drosophila melanogaster (fruit flies
)
The
first animals sent into space were fruit flies aboard a
U.S.-launched V-2 rocket on February 20, 1947 from White Sands
Missile Range, New Mexico.The purpose of the experiment was to
explore the effects of radiation exposure at high altitudes. The
rocket reached 68 miles (109 km) in 3 minutes and 10 seconds, past
both the U.S. Air Force 50-mile and the international 100 km
definitions of the boundary of space. The Blossom capsule was
ejected and successfully deployed its parachute. The fruit flies
were recovered alive. Other V2 missions carried biological samples,
including moss.
Laika (Russian ), meaning "Barker"; c. 1954 – November 3, 1957)
was a Soviet space dog who became one of the first animals in space, and the first animal to orbit the Earth.On November 3, 1957, the second-ever orbiting spacecraft carried the first animal into orbit, the dog Laika, launched aboard the Soviet Sputnik 2 spacecraft (nicknamed 'Muttnik' in the West). Laika died during the flight, as was intended because the technology to return from orbit had not yet been developed. At least 10 other dogs were launched into orbit
On July 22, 1951, the Soviet Union launched the R-1 IIIA-1 flight,
carrying the dogs Tsygan , "Gypsy")and Dezik into space, but
not into orbit.These two dogs were the first living higher
organisms successfully recovered from a spaceflight.Both space dogs
survived the flight, although one would die on a subsequent flight.
The U.S. launched mice aboard spacecraft later that year; however,
they failed to reach the altitude for true
spaceflight.
Monkey in space
((Space monkey "Baker" rode a Jupiter IRBM into space in 1959
):
Monkeys
Able and Baker became the first monkeys to survive spaceflight
after their 1959 flight. On May 28, 1959, aboard Jupiter IRBM
AM-18, were a 7-pound (3.18 kg) American-born rhesus monkey, Able,
and an 11 ounce (310 g) squirrel monkey from Peru, Baker. The
monkeys rode in the nose cone of the missile to an altitude of 360
miles (579 km) and a distance of 1,700 miles (2,735 km) down the
Atlantic Missile Range from Cape Canaveral, Florida. They withstood
forces 38 times the normal pull of gravity and were weightless for
about 9 minutes. A top speed of 10,000 mph (16,000 km/h) was
reached during their 16-minute flight. The monkeys survived the
flight in good condition. Able died four days after the flight from
a reaction to anesthesia, while undergoing surgery to remove an
infected medical electrode. Baker lived until November 29, 1984, at
the US Space and Rocket Center in Huntsville,
Alabama.
What is Galaxy ?
A galaxy is, by definition, any large collection of stars that can
be recognized as a distinct physical entity. In terms of the number
of stars, a small 'dwarf irregular' galaxy like the Small
Magellanic Cloud, has about one billion stars in it, but there are
even smaller systems that are recognized as galaxies such as the
Leo I and II dwarf galaxies with about 1 million stars in them, and
the Draco System with a few hundred thousand stars in it. The
largest star cluster, a globular cluster called Messier 15 has
about 6 million stars, so we see that for small galaxies, there is
a blurring together of what we mean by a galaxy and a large star
cluster. In addition to their mass and numbers of stars, a galaxy
is a collection of stars and gas which move through the universe
independently of the Milky Way. Globular clusters are roundish
swarms of stars that orbit the Milky Way, while the Leo and Draco
Systems seem to be independent collections of stars.
Galaxies are the places where gas turns into luminous stars,
powered by nuclear reactions that also produce most of the chemical
elements. But the gas and stars are
only the tip of an iceberg: a galaxy consists mostly of dark
matter, which we know only by the pull of its gravity. The ages,
chemical composition and motions of the
stars we see today, and the shapes that they make up, tell us about
each galaxy’s past life. This book presents the astrophysics of
galaxies since their beginnings in
the early Universe. This Second Edition is extensively illustrated
with the most recent observational data. It includes new sections
on galaxy clusters, gamma
ray bursts and supermassive black holes. Chapters on the
large-scale structure and early galaxies have been thoroughly
revised to take into account recent discoveries
such as dark energy.The authors begin with the basic properties of
stars and explore the Milky Way before working out towards nearby
galaxies and the distant Universe, where galaxies can be seen in
their early stages. They then discuss the structures of galaxies
and how galaxies have developed, and relate this to the evolution
of
the Universe. The book also examines ways of observing galaxies
across the electromagnetic spectrum, and explores dark matter
through its gravitational pull
on matter and light.
Facts about Galaxies:-
Galaxy Facts
•Galaxy is derived from the Greek word meaning milk.
•Our solar system is in a galaxy called the Milky Way.
•Away from light pollution a spiral arm of the Milky Way can be
seen in the night sky with the naked eye.
•The Milky Way is 100,000 light years across and is thought to have
formed 10 to 12 billion years ago.
•Earth is located 26,000 light years from the center of the Milky
Way.
•The Milky Way rotates once every 250 million years.
•There are around 200 billion stars in our galaxy.
•There are approximately 100 billion galaxies in the visible
Universe.
•The nearest spiral galaxy to the Milky Way is Andromeda, it is 2.5
million light years from Earth.
•Andromeda is the furthest object that can be seen with the naked
eye.
•At the center of most galaxies there is a supermassive black hole
which can be millions of times more massive than our
sun.
Age of Galaxy
How do you know galaxies are moving apart ?Light reaching us from distant receding galaxies has its absorption lines shifted toward the red end of the spectrum. This indicates that the galaxy is moving away from the Earth.The red shift indicates that the universe is expanding
Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million
light-years from Earth in the Andromeda constellation. Also known
as Messier 31, M31, or NGC 224, it is often referred to as the
Great Andromeda Nebula in older texts.
Distance to Earth: 2,538,000 light years
Apparent mass: ~1,230 billion M?
Age: 9 billion years
Constellation: Andromeda
Stars: 1 trillion
Coordinates: RA 0h 42m 44s | Dec 41° 16.152'
The Milky Way
The Milky Way is the galaxy that contains our Solar System. Its
name “milky” is derived from its appearance as a dim glowing band
arching across the night sky in which the naked eye cannot
distinguish individual stars.
Apparent mass: ~1,250 billion M?
Age: 13.2 billion years
Stars: 300 billion
Location : The solar system is located within the Milky Way Galaxy
on a branch called the Orion Spur
Distance from Earth to the galactic center : 26,000 light
years in the direction of Sagittarius
Diameter : 100,000 light years across
Name of our galaxy is known as the Milky Way galaxy. The Milky Way
is a barred spiral galaxy and is part of the Local Group of
galaxies. Ours is merely is one of billions of galaxies in the
observable universe. Our sun is 25,000 light years from the center
of the Milky Way. The oldest star in the galaxy is 13.2 billion
years old.The stellar disk of the Milky Way Galaxy is approximately
100,000 light years in diameter and is about 1,000 light years
thick. It is estimated to contain up to 400 billion stars. The
exact figure depends on the number of very low-mass stars, which is
difficult to determine. The stellar disc does not have a sharp
edge, a radius beyond which there are no stars; however, the number
of stars drops slowly with distance from the center. Beyond a
radius of roughly 40,000 light years the number of stars
drops much faster the farther you get from the center. Beyond the
stellar disk is a much thicker disk of gas that is estimated to be
12,000 light years thick. twice the previously accepted
value.
In 2007, the star HE 1523-0901 was estimated to be about 13.2
billion years old. The galaxy is thought to be just slightly older.
The estimate of this star’s age was determined using the UV-Visual
Echelle Spectrograph of the Very Large Telescope to measure the
relative strengths of spectral lines caused by the presence of
thorium and other elements created by the R-process. The line
strengths yield abundances of different elemental isotopes from
which an estimate of the age of the star can be derived using
nucleocosmochronology
Types of Galaxies
The existence of other galaxies was established only in the 1920s.
Before that, they were listed in catalogues of nebulae: objects
that appeared fuzzy in a telescope
and were therefore not stars. Better images revealed stars within
some of these ‘celestial clouds’. Using the newly opened 100
telescope on MountWilson,Edwin
Hubble was able to find variable stars in the Andromeda ‘nebula’
M31.He showed that their light followed the same pattern of
changing brightness as
Cepheid variable stars within our Galaxy. Assuming that all these
stars were of the same type, with the same luminosities, he could
find the relative distances from
Equation 1.1. He concluded that the stars of Andromeda were at
least 300 kpc from the Milky Way, so the nebula must be a galaxy in
its own right. We now
know that the Andromeda galaxy is about 800 kpc away.Hubble set out
his scheme for classifying the galaxies in a 1936 book, The Realm
of the Nebulae. With later additions and modifications, this system
is still used today; Hubble recognized three main types of galaxy:
ellipticals,lenticulars, and spirals, with a fourth class, the
irregulars, for galaxies that would not fit into any of the other
categories.Elliptical galaxies are usually smooth, round, and
almost featureless, devoid of
such photogenic structures as spiral arms and conspicuous dust
lanes. Ellipticals are generally lacking in cool gas and
consequently have few young blue stars.
Though they all appear approximately elliptical on the sky,
detailed study shows that large bright ellipticals have rather
different structures from their smaller and
fainter counterparts.Ellipticals predominate in rich clusters of
galaxies, and the largest of them, the cD galaxies, are found in
the densest parts of those clusters. Around an elliptical core, the
enormous diffuse envelope of a cD galaxy may stretch for hundreds
of kiloparsecs; these systems can be up to 100 times more luminous
than the Milky Way. Normal or giant ellipticals have luminosities a
few times that of the Milky Way, with characteristic sizes of tens
of kiloparsecs. The stars of these bright ellipticals show little
organized motion, such as rotation; their orbits about the galaxy
center are oriented in random directions.
In less luminous elliptical galaxies, the stars have more rotation
and less random motion. Often there are signs of a disk embedded
within the elliptical body.
The very faintest ellipticals, with less than ~1/10 of the Milky
Way’s luminosity, split into two groups. The first comprises the
rare compact ellipticals,like
the nearby system M32. The other group consists of the faint
diffuse dwarf elliptical (dE) galaxies, and their even less
luminous cousins the dwarf spheroidal
(dSph) galaxies, which are so diffuse as to be scarcely visible on
sky photographs. The dE and dSph galaxies show almost no ordered
rotation.Lenticular
galaxies show a rotating disk in addition to the central elliptical
bulge, but the disk lacks any spiral arms or extensive dust lanes.
These galaxies
are labelled S0 (pronounced ‘ess-zero’), and they form a transition
class between llipticals and spirals. They resemble ellipticals in
lacking extensive gas and dust,and
in preferring regions of space that are fairly densely populated
with galaxies; but they share with spirals the thin and
fast-rotating stellar disk.
The left panel of Spiral galaxies are named for their bright spiral
arms, which are especially conspicuous in the blue light that was
most easily recorded by early
photographic plates. The arms are outlined by clumps of bright hot
O and B stars, and the compressed dusty gas out of which these
stars form. About half of all spiral
and lenticular galaxies show a central linear bar: the barred
systems SB0, SBa ,SBd form a sequence parallel to that of the
unbarred galaxies. Along the sequence
from Sa spirals to Sc and Sd, the central bulge becomes less
important relative to the rapidly rotating disk, while the spiral
arms become more open and the fraction
of gas and young stars in the disk increases. Our Milky Way is
probably an Sc galaxy, or perhaps an intermediate Sbc type; M31 is
an Sb. On average, Sc and
Sd galaxies are less luminous than the Sa and Sb systems, but some
Sc galaxies are still brighter than a typical Sa spiral.
At the end of the spiral sequence, in the Sd galaxies, the spiral
arms become more ragged and less well ordered. The Sm and SBm
classes are Magellanic
spirals, named after their prototype, which is our Large Magellanic
Cloud; . In these, the spiral is often reduced to a single stubby
arm. As the
galaxy luminosity decreases, so does the speed at which the disk
rotates; dimmer galaxies are less massive. The Large Magellanic
Cloud rotates at only 80 km s-1,
a third as fast as the Milky Way. Random stellar motions are also
diminished in the smaller galaxies, but even so, ordered rotational
motion forms a less important
part of their total energy.We indicate this that by placing these
galaxies to the left of the Sd systems.The
terms ‘early type’ and ‘late type’ are often used to describe the
position of galaxies along the sequence from elliptical galaxies
through S0s to Sa, Sb, and Sc
spirals. Some astronomers once believed that this progression might
describe the life cycle of galaxies, with ellipticals turning into
S0s and then spirals. Although
this hypothesis has now been discarded, the terms live on.
Confusingly, ‘earlytype’ galaxies are full of ‘late-type’ stars,
and vice versa.Hubble
placed all galaxies that did not fit into his other categories in
the irregular class. Today, we use that name only for small blue
galaxies which lack
any organized spiral or other structure . The smallest of the
irregular galaxies are called dwarf irregulars; they differ from
the dwarf spheroidals by
having gas and young blue stars. It is possible that dwarf
spheroidal galaxies are just small dwarf irregulars which have lost
or used up all of their gas. Locally,
about 70% of moderately bright galaxies are spirals, 30% are
elliptical or S0 galaxies, and 3% are irregulars.Other galaxies
that Hubble would have called irregulars include the starburst
galaxies. These systems have formed many stars in the recent past,
and their disturbed appearance results in part from gas thrown out
by supernova explosions.
Spiral and S0 galaxies
The main feature of a spiral or S0 galaxy is its conspicuous
extended stellar disk. Stars in the disk of a large spiral galaxy,
like our MilkyWay, follow nearly circular orbits with very little
random motion. Ordered rotation accounts for almost all the energy
of motion, with random speeds contributing less than ~5%: the disk
is dynamically ‘cold’. In smaller galaxies, random motions are
proportionally larger,but most of the disk’s kinetic energy is
still in rotation. Because the stars have little vertical motion
perpendicular to the disk plane, the disk can be quite thin.Spiral
galaxies are distinguished from S0 systems by the multi-armed
spiral pattern in the disk. The disks of spiral galaxies still
retain some gas, whereas S0 systems have lost their disk gas, or
converted it into stars. Both S0 and spiral galaxies can show a
central linear bar , the sequence of barred galaxies SB0, SBa, . .
. , SBm runs parallel to the ‘unbarred’ sequence S0, Sa, . . .Apart
from the bar and spiral arms, the stellar disks of large galaxies
are usually fairly round; but many smaller systems are quite
asymmetric.
Most giant disk galaxies – those with MB ~<-19 or LB ~>6 ×
109L – are composite systems. Many of them probably have a
metal-poor stellar halo
like that of the Milky Way . But the halo accounts for only a few
percent of the galaxy’s light, and is spread over an enormous
volume; so the surface brightness is low, making it difficult to
study. The dense inner bulge is prominent in the Sa and S0 systems,
less important in Sb and Sc galaxies, and absent in the Sd and Sm
classes. Bulge stars have considerable random motions, and they are
much more tightly packed than in the disk: near the Sun, the
density of stars is n ~ 0.1 pc-3, whereas in bulges it is often 10
000 times higher. Bulges are generally rounder than the very
flattened disks. They tend to be gas-poor, except for their
innermost regions; in some respects, they are small elliptical
galaxies placed inside a disk. The central hundred parsecs of the
bulge may accumulate enough gas to fuel violent bursts of star
formation. As in our Milky Way, the centers of many bulges host
nuclear star clusters, the densest stellar systems. In some nuclei,
we find massive compact central objects, which are probably black
holes . Spirals are the most common of the giant galaxies, and
produce most of the visible light in the local Universe. In the
opening section we investigate the stellar content of the disks of
spiral and S0 galaxies; Section 5.2 considers the gaseous
component, and its relationship to the stars. In Section 5.3 we
discuss the rotation curves of spiral galaxies, and what these
reveal about the gravitational forces. In most spirals, the force
required to maintain the outermost disk material in its orbit
cannot be accounted for by the visible portion of the galaxy, its
stars and gas. The difference is attributed to ‘dark’ material,
which we detect only by its gravity. We then pause, in Section 5.4,
to consider how much the scheme of Figure 1.11, classifying
galaxies according to their appearance in visible light, can tell
us about their other properties. Spiral arms and galactic bars form
the topic of Section 5.5; these common and prominent features prove
surprisingly difficult to understand. In Section 5.6 we discuss
bulges and nuclei, and speculate on how they are related to the
rest of the galaxy.
Elliptical Galaxy
Elliptical galaxies
look like simple objects; but they are not. As their name
implies, they appear round on
the sky; the light is smoothly distributed, and they lack
the
bright clumps of
young blue stars and patches of obscuring dust which are
such
obvious features of
spiral galaxies. Ellipticals are almost devoid of cool gas,
except
at the very center;
in contrast to S0 systems, they have no prominent disk.
Their
smooth appearance
suggests that, like the molecules of air in a room, their
stars
have had time to
reach a well-mixed equilibrium state. As with stars on the
main
sequence, we would
expect the properties of elliptical galaxies to reflect the
most
probable state of a
fairly simple system, with ‘no surprises’.Instead, detailed
studies reveal a bewildering complexity. Elliptical galaxies
cover a
huge range of luminosity and of light concentration. Some
ellipticals rotate
fast, others hardly
at all. Some appear to be oblate (grapefruit shaped), while
othershave a triaxial shape
with three unequal axes, like a squashed (American or
rugby)
football.
These properties are interlinked: luminous ellipticals are more
likely to
be triaxial, slowly
rotating, and also strong X-ray sources, while the less
luminoussystems are oblate
and relatively rapidly rotating, and have dense stellar cusps
at
their
centers.Itwas a mistake to
think that elliptical galaxies might be close to an
equilibrium
state, because
stellar systems have a very long memory. Most of a galaxy’s
stars
have made fewer than
100 orbits about the center; we saw in Section 3.2 that the
relaxation time
required to randomize their motions is far greater than the
age
of the Universe. If a
galaxy was assembled in a triaxial shape, or with a dense
central
cusp, these characteristics would not yet have been erased. The
variety
among
elliptical galaxies suggests that they originated by a number of
different
pathways. Present-day
elliptical galaxies are ‘fossils’ of the earlier Universe;
our
task is to
reconstruct their birth and youthful star-forming lives from the
old lowmass
stars that
remain.
We begin this chapter
with a section on photometry: how the images of elliptical
galaxies
appear in visible light, and what this tells us about the
distribution
of stars within
them. discusses stellar motions, and how the rotation of an
elliptical galaxy is linked to its other properties. We consider
what stellar
orbits would be
possible in a triaxial galaxy, with three unequal axes. In
we look
at the stellar populations of elliptical galaxies and at
their
gaseous content.
Elliptical galaxies are quite rich in interstellar gas, but that
gas
is much hotter than
the gas in disk systems; it can be studied only in X-rays. the dark
matter in elliptical galaxies and the black holes at
their centers.