Category The Universe, Exploring the Universe, Solar System, The Moon, Space, Space Travel

Space launchers are rockets that carry payloads into space. Just as there are many sizes of truck to carry different goods from place to place, there are many different space launchers, each suited to different purposes. Rockets such as the Mercury-Atlas were designed to be small and light, as they only had to carry one man. Russia’s Soyuz series are incredibly powerful, able to carry 20 tonnes into a low-Earth orbit. NASA’s Saturn V was designed to be powerful enough to carry three men to the Moon.

NASA’s Space Launch System, or SLS, is an advanced launch vehicle that provides the foundation for human exploration beyond Earth’s orbit. With its unprecedented power and capabilities, SLS is the only rocket that can send Orion, astronauts and large cargo to the Moon on a single mission.

Offering more payload mass, volume capability and energy to speed missions through space than any current launch vehicle, SLS is designed to be flexible and evolvable and will open new possibilities for payloads, including robotic scientific missions to places like the Moon, Mars, Saturn and Jupiter.

Engineers are making progress toward delivering the first SLS rocket to NASA’s Kennedy Space Center in Florida for its first launch.

Picture Credit : Google

Galaxies themselves may appear to be enormous, but even they do not exist independently in space. They gather together in groups — from pairs to clusters that can contain thousands of galaxies. The Milky Way is only one of a cluster of around 30 galaxies that make up the Local Group, an enormous collection of galaxies that stretches over millions of light years. The largest known cluster is the Virgo cluster, which contains over 2000 galaxies. Just as gravity causes galaxies to form clusters, it also brings clusters together to form superclusters. These are the largest structures in the Universe, stretching hundreds of millions of light years across space.

Groups of galaxies are the smallest aggregates of galaxies. They typically contain no more than 50 galaxies in a diameter of 1 to 2 megaparsecs (Mpc)(see 1022 m for distance comparisons). Their mass is approximately 1013 solar masses. The spread of velocities for the individual galaxies is about 150 km/s. However, this definition should be used as a guide only, as larger and more massive galaxy systems are sometimes classified as galaxy groups. Groups are the most common structures of galaxies in the universe, comprising at least 50% of the galaxies in the local universe. Groups have a mass range between those of the very large elliptical galaxies and clusters of galaxies.  Our own Galaxy, the Milky Way, is contained in the Local Group of more than 54 galaxies.

In July 2017 S. Paul, R. S. John et al. defined clear distinguishing parameters for classifying galaxy aggregations as ‘galaxy groups’ and ‘clusters’ on the basis of scaling laws that they followed. According to this paper, galaxy aggregations less massive than 8 × 1013 solar masses are classified as Galaxy groups.

Clusters are larger than groups, although there is no sharp dividing line between the two. When observed visually, clusters appear to be collections of galaxies held together by mutual gravitational attraction. However, their velocities are too large for them to remain gravitationally bound by their mutual attractions, implying the presence of either an additional invisible mass component, or an additional attractive force besides gravity. X-ray studies have revealed the presence of large amounts of intergalactic gas known as the intra-cluster medium. This gas is very hot, between 107K and 108K, and hence emits X-rays in the form of bremsstrahlung and atomic line emission.

The total mass of the gas is greater than that of the galaxies by roughly a factor of two. However, this is still not enough mass to keep the galaxies in the cluster. Since this gas is in approximate hydrostatic equilibrium with the overall cluster gravitational field, the total mass distribution can be determined. It turns out the total mass deduced from this measurement is approximately six times larger than the mass of the galaxies or the hot gas. The missing component is known as dark matter and its nature is unknown. In a typical cluster perhaps only 5% of the total mass is in the form of galaxies, maybe 10% in the form of hot X-ray emitting gas and the remainder is dark matter. Brownstein and Moffat use a theory of modified gravity to explain X-ray cluster masses without dark matter. Observations of the bullet Cluster are the strongest evidence for the existence of dark matter; however, Brownstein and Moffat have shown that their modified gravity theory can also account for the properties of the cluster.

Galaxies are classified using a very simple code that describes their basic shape. “E” is used to describe an elliptical galaxy, and a number from 0 to 7 is added to further define its form. An EO galaxy looks like a ball, whereas an E7 galaxy resembles a short, fat sausage. Spiral galaxies are defined by the letter “S”, and barred spiral galaxies by the letters “BS”. Both these forms of galaxy are given further definition by the addition of a letter a, b, .c or d. Galaxies with tightly wound arms are labelled Sa, and galaxies with looser arms are labelled Sd.

Galaxies are classified by shape. There are three general types: elliptical, spiral, and irregular. Perhaps the most familiar kind of galaxy is spiral galaxies. They have a distinctive shape with spiral arms in a relatively flat disk and a central “bulge”. The bulge has a large concentration of stars. The arms and bulge are surrounded by a faint halo of stars. The bulge and halo consist mainly of older stars, where spiral arms have more gas, dust and younger stars. Our Milky Way Galaxy is a spiral galaxy.

Some spiral galaxies are what we call “barred spirals” because the central bulge looks elongated – like a bar. In barred spirals, the spiral arms of the galaxy appear to spring out of the ends of the bar.

As their name suggests, elliptical galaxies are round or oval, with stars distributed fairly uniformly throughout. They have a bulge and halo, like spiral galaxies, but don’t have the flat disk of stars. The stars in ellipticals tend to be older.

Irregular galaxies have no identifiable shape or structure to them. They are often chaotic in appearance, without a bulge or any trace of spiral arms. The different shapes and orientation of galaxies are a result of their history, which may have included interactions with other galaxies.

Artist’s concept of Edwin Hubble’s galaxy classification system, created to classify galaxies depending on their appearance, This system is sometimes called Hubble’s Tuning Fork. At the left are elliptical galaxies, which are classified depending on how round they appear. The scale goes from E0 (the roundest) to E7, the most elliptical. Further to the right are lenticular galaxies, which are an intermediary class between ellipticals and spirals (classified SA0 or SB0, depending on if they have a bar at the core). To the right are the spiral galaxies, and they are classified depending on how tightly coiled (Sa, Sb and Sc) the spiral arms are (top branch), and if their core hosts a barred shape (bottom branch). The barred galaxies get the classification SBa, SBb and SBc, where SBa has the most tightly coiled arms.

Galaxies come in all shapes and sizes, but astronomers divide them into just a few main types. More than half of all galaxies are elliptical, named because of their egg-like shape. They are made up of large numbers of old, red stars and have very little gas and dust with which to make new ones. Around a third of all galaxies are spiral in shape, like the Milky Way. Old stars are packed tightly in their centres, while new stars are continually being born from the large amounts of gas and dust in their spiral arms. Some spiral galaxies are classed separately because their nucleus is elongated into a bar. This bar is made up of stars in motion, and the spiral arms extend from the ends of the bar. Some galaxies cannot be classed as either spirals or ellipticals because they have no recognizable shape. These galaxies are called irregulars, and are full of gas in which new stars are forming.

In our universe are four identified types of galaxies. These galaxies are composed of stars, gas and dust held together with gravitational forces. Each galaxy type is named for its shape, making it easy to identify which type of galaxy you are looking at. You may already be familiar with the galaxies: spiral, barred spiral, elliptical and irregular. These fascinating galaxies were each formed from a unique mixture of gases and matter that came together, painting our magnificent galaxies, each one a unique work of artistic beauty.

Spiral Galaxy – Spiral galaxies are characterized by a distinct flattened spiral disk with a bright center called the nucleus. Our own Milky Way is a spiral galaxy. Spiral galaxies are represented by the letter S and are divided into four subgroups. These are S0, Sa, Sb, and Sc. S0 galaxies have a bright nucleus but have no spiral arms. Sa galaxies have spiral arms that are wound tightly around the nucleus while the arms of Sc galaxies are wound much more loosely.

Barred Spiral Galaxy – A barred spiral galaxy is very similar to a spiral with one important difference. The arms spiral out from a straight bar of stars instead of from the center. About one third of all spiral galaxies are barred spiral in shape. Barred spiral galaxies are represented by the letters SB and are arranges into three subgroups according to the openness of the arms. These subgroups are labeled SBa, SBb, and SBc. SBa galaxies have a short bar of stars extending from the center while SBc galaxies have a long, well-defined bar. Our own Milky Way galaxy is now believed to be a barred spiral galaxy.

Elliptical Galaxy – Elliptical galaxies vary in shape from completely round to extremely elongated ovals. Unlike spiral galaxies, they have no bright nucleus at their center. Elliptical galaxies are represented by the letter E and are divided into seven subgroups according to their shape. These subgroups are labeled E0 to E7. E0 galaxies nearly circular in shape while E7 galaxies are extremely elongated or stretched out.

Irregular Galaxy – A fourth type of galaxy is known as the irregular galaxy. These galaxies have no discernible shape or structure. Irregular galaxies are divided into two classes, Im and IO. Im class galaxies are the most common and show just a hint of structure. Sometimes the faint remnants of spiral arms can be seen. IO class galaxies are completely chaotic in form. The large and small Magellanic Clouds are examples of Im class irregular galaxies.

Astronomers cannot see what lies at the centre of the Milky Way because of the large amounts of dust in the way. Radio waves are not affected by dust, however, so scientists have been able to make detailed maps of the galaxy. They have found that at the centre of the Milky Way lies an enormous black hole —as large as Jupiter’s orbit around the Sun — which is sucking in matter and pouring out energy with the strength of almost 100 million Suns.

If you look up on a dark, clear night, away from city lights, you may see a wide band of faint light stretching above you, stiller than a cloud and glittering with densely packed stars. Translated from the Ancient Greek as “Milky Way” for resembling spilled milk on the sky, that band of light is the center of our galaxy. At its center, surrounded by 200-400 billion stars and undetectable to the human eye and by direct measurements, lies a supermassive black hole called Sagittarius A, or Sgr A* for short.

The Milky Way has the shape of a spiral and rotates around its center, with long curling arms surrounding a slightly bulging disk. It’s on one of these arms close to the center that the sun and Earth are located. Scientists estimate that the galactic center and Sgr A* are around 25,000 to 28,000 light-years away from us. The entire galaxy is around 100,000 light-years across.

A supermassive black hole is the largest type of black hole in a galaxy, with a mass millions of times that of our sun. Though it can’t be imaged directly because black holes pull in all light, scientists have inferred its presence by looking at the speed and motion of stars and matter close to the galactic center. They have inferred that the movements are influenced by the gravitational pull of a black hole.

No one knows how the black holes at the center of galaxies form, but some suspect that they may begin as a cluster of smaller black holes that merge, or as a smaller black hole that consumes enough matter to become a supermassive one.

Just as the sun’s gravity holds the objects of the Solar System in their orbits, the gravitational pull of the Milky Way keeps _two smaller galaxies in tow. The two Magellanic Clouds consist of thousands of star clusters that orbit the Milky Way every 1.5 billion years. The Large Magellanic Cloud (right) is made of the same mix of gas and stars as the Milky Way, but is less than one-twentieth as large. The Small Magellanic Cloud is slowly being pulled apart by the gravity of our galaxy.

Our sun is part of a massive collection of stars in the Milky Way galaxy. These hundreds of billions of stars orbit the galaxy’s center. But did you know that there are things that are even bigger orbiting the Milky Way’s center? Other galaxies orbit it too! These less massive galaxies have their own impressive collection of stars, which all orbit their own center; but the galaxies and everything in them orbit our galaxy too. It’s as if our galaxy is the sun and those other galaxies are planets. Astronomers call them “satellite galaxies.”

The Milky Way has a number of satellite galaxies, but the biggest one is the Large Magellanic Cloud. It is about 163,000 light-years away and around 1/100th the size of the Milky Way. Unlike our spiral galaxy, this one lacks a clean spiral shape. Some scientists think that is because the Milky Way and other galaxies are pulling and warping it.

In terms of distance, there are two contenders for closest satellite galaxy. One group of stars is small enough that astronomers consider it a “dwarf galaxy.” The other group is so close that they still debate whether or not it is part of our galaxy or its own dwarf galaxy. Astronomers have named the one that everyone agrees on the Sagittarius Dwarf Spheroidal Galaxy. It’s about 50,000 light-years away from the Milky Way center. It orbits over the top and down below the disk of our galaxy, like a ring over a spinning top.

But there is something even closer to our Milky Way—a cluster of stars named by some to be the Canis Major Dwarf Galaxy. Scientists estimate that it contains around a billion stars. It is so close to the edge of the Milky Way that it is closer to our solar system than to our galaxy’s center. It’s about 25,000 light-years away from us.

Some scientists don’t think the Canis Major cluster of stars is actually its own galaxy or dwarf galaxy. Instead they think it is just a dense area of faraway stars that are still part of the Milky Way. Either way, it is clear that this bunch of stars has been pulled very close to our Milky Way by our galaxy’s massive gravity. Over time, this could be the fate of other satellite galaxies in the area. They could all one day merge into an even larger Milky Way galaxy!