Galaxies in the Universe

Our Universe is 10 times more crowded with galaxies than first thought

Astronomers defined a new number of galaxies  in the universe.The observable Universe is a lot more crowded than astronomers previously thought and may contain more than 2,000 billion galaxies.



A deep-sky census assembled from surveys taken by the Hubble Space Telescope found that the observable universe has at least ten times more galaxies than we were aware of. Astronomers at theUniversity of Nottingham discovered that in the early Universemany small and faint galaxies were crammed into volumes of space previously thought to be only sparsely populated by galaxies.




The majority of galaxies observed were relatively tiny, with masses comparable to those of the Milky Way’s own satellite galaxies. The largest of which is only a fifth the size of our galaxy.

 Important Galaxies                                                                                 

1.Milky Way Galaxy

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 whose individual stars cannot be distinguished by the naked eye.The Milky Way is a barred spiral galaxy that has a diameter usually considered to be about 100,000–120,000 light-years but may be 150,000–180,000 light-years. The Milky Way is estimated to contain 100–400 billion stars. There are likely at least 100 billion planets in the Milky Way. The Solar System is located within the disk, about 27,000 light-years from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust called the Orion Arm.



2.Andromeda Galaxy

The Andromeda Galaxy , also known as Messier 31, M31, or NGC 224, is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth. It is the nearest major galaxy to the Milky Way and was often referred to as theGreat Andromeda Nebula in older texts. It received its name from the area of the sky in which it appears, the constellation of Andromeda, which was named after the mythological princess Andromeda.The Milky Way and Andromeda are expected to collide in 3.75 billion years, eventually merging to form a giant elliptical galaxy or perhaps a large disc galaxy.The apparent magnitude of the Andromeda Galaxy, at 3.4, is among the brightest of the Messier objects, making it visible to the naked eye on moonless nights, even when viewed from areas with moderate light pollution.


3.Antennae Galaxies


The Antennae Galaxies, also known as NGC 4038/NGC 4039, are a pair of interacting galaxies in the constellation Corvus. They are currently going through a starburst phase, in which the collision of clouds of gas and dust, with entangled magnetic fields, causes rapid star formation. They were discovered by William Herschel in 1785.The nuclei of the two galaxies are joining to become one giant galaxy. Most galaxies probably undergo at least one significant collision in their lifetimes. This is likely the future of our Milky Way when it collides with the Andromeda Galaxy.About 1.2 billion years ago, the Antennae were two separate galaxies. NGC 4038 was a barred spiral galaxy and NGC 4039 was a spiral galaxy. Before the galaxies collided, NGC 4039 was larger than NGC 4038. 900 million years ago, the Antennae began to approach one another, looking similar to NGC 2207 and IC 2163. 600 million years ago, the Antennae passed through each other, looking like the Mice Galaxies. 300 million years ago, the Antennae's stars began to be released from both galaxies. Today the two streamers of ejected stars extend far beyond the original galaxies, resulting in the antennae shape.

4.Black Eye Galaxy


The Black Eye Galaxy (also called Evil Eye Galaxy; designated Messier 64, M64, or NGC 4826) is a galaxy which was discovered by Edward Pigott in March 1779, and independently by Johann Elert Bode in April of the same year, as well as by Charles Messier in 1780. It has a spectacular dark band of absorbing dust in front of the galaxy's bright nucleus, giving rise to its nicknames of the "Black Eye" or "Evil Eye" galaxy. M64 is well known among amateur astronomers because of its appearance in small telescopes. It is a spiral galaxy in the Coma Berenices constellation.

5.Cartwheel Galaxy


The Cartwheel Galaxy (also known as ESO 350-40) is a lenticular galaxy and ring galaxy about 500 million light-years away in the constellation Sculptor. It is an estimated 150,000 light-years across, has a mass of about 2.9–4.8 × 109 solar masses, and rotates at217 km/s.It was discovered by Fritz Zwicky in 1941. Zwicky considered his discovery to be "one of the most complicated structures awaiting its explanation on the basis of stellar dynamics." The galaxy was once a normal spiral galaxy before it apparently underwent a head-on collision with a smaller companion approximately 200 million years ago (i.e., 200 million years prior to the image). When the nearby galaxy passed through the Cartwheel Galaxy, the force of the collision caused a powerful shock wave through the galaxy, like a rock being tossed into a sandbed. Moving at high speed, the shock wave swept up gas and dust, creating a starburst around the galaxy's center portion that were unscathed. This explains the bluish ring around the center, brighter portion. It can be seen that the galaxy is beginning to retake the form of a normal spiral galaxy, with arms spreading out from a central core.


6.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. However, the gravitational disruptions caused by such an event could cause a wave of star formation to move through the larger galaxy. Other astronomers think that rings are formed around some galaxies when external accretion takes place. Star formation would then take place in the accreted material because of the shocks and compressions of the accreted material.

7.Mayall's Object

Mayall's Object (also classified under the Atlas of Peculiar Galaxies as Arp 148) is the result of two colliding galaxies located 500 million light years away within the constellation of Ursa Major. It was discovered by Nicholas U. Mayall of the Lick Observatory on 13 March 1940, using the Crossley reflector.When first discovered, Mayall's Object was described as a peculiar nebula, shaped like a question mark. Originally theorized to represent a galaxy reacting with the intergalactic medium,it is now thought to represent the collision of two galaxies, resulting in a new object consisting of a ring-shaped galaxy with a tail emerging from it. It is thought that the original collision between the two original galaxies created a shockwave that initially drew matter into the center which then formed the ring.

8.Sunflower Galaxy

Messier 63 (also known as M63, NGC 5055, or the Sunflower Galaxy) is a spiral galaxy in the constellation Canes Venaticiconsisting of a central disc surrounded by many short spiral arm segments. M63 is part of the M51 Group, a group of galaxies that also includes M51 (the 'Whirlpool Galaxy'). M63 is an active galaxy with a LINER nucleus. M63 was discovered by Pierre Méchain on June 14, 1779. The galaxy was then listed by Charles Messier as object 63 in theMessier Catalogue.In the mid-19th century, Lord Rosse identified spiral structures within the galaxy, making this one of the first galaxies in which such structure was identified.In 1971, a supernova with a magnitude of 11.8 appeared in one of the arms of M63.



9.Bode's Galaxy


Messier 81 (also known as NGC 3031 or Bode's Galaxy) is a spiral galaxy about 12 million light-years away in the constellationUrsa Major. Due to its proximity to Earth, large size and active galactic nucleus (which harbors a 70 million solar mass (M☉) supermassive black hole), Messier 81 has been studied extensively by professional astronomers. The galaxy's large size and relatively high brightness also make it a popular target for amateur astronomers.Messier 81 was first discovered by Johann Elert Bode in 1774. Consequently, the galaxy is sometimes referred to as "Bode's Galaxy". In 1779, Pierre Méchain and Charles Messier reidentified Bode's object, which was subsequently listed in the Messier Catalogue. Only one supernova has been detected in Messier 81.The supernova, named SN 1993J, was discovered on 28 March 1993 by F. Garcia in Spain. At the time, it was the second brightest supernova observed in the 20th century.

10.Cigar Galaxy

Messier 82 (also known as NGC 3034, Cigar Galaxy or M82) is a starburst galaxy about 12 million light-years away in the constellation Ursa Major and a member of the M81 Group. It is about five times more luminous than the whole Milky Way and has a center one hundred times more luminous than our galaxy's center. The starburst activity is thought to have been triggered by interaction with neighboring galaxy M81. As the closest starburst galaxy to our own, M82 is the prototypical example of this galaxy type. SN 2014J, a type Ia supernova, was discovered in the galaxy on 21 January 2014,. In 2014, in studying M82, scientists discovered the brightest pulsar yet known, designated M82 X-2.

11.NGC 2207 and IC 2163
NGC 2207 and IC 2163 are a pair of colliding spiral galaxies about 80 million light-years away in the constellation Canis Major. Both galaxies were discovered by John Herschel in 1835. The larger spiral, NGC 2207, is classified as an intermediate spiral galaxy exhibiting a weak inner ring structure around the central bar. The smaller companion spiral, IC 2163, is classified as a barred spiral galaxy that also exhibits a weak inner ring and an elongated spiral arm that is likely being stretched by tidal forces with the larger companion. Both galaxies contain a vast amount of dust and gas, and are beginning to exhibit enhanced rates of star formation, as seen in infrared images. So far, four supernovae have been observed in NGC 2207. NGC 2207 is in the process of colliding and merging with IC 2163. But unlike the Antennae or the Mice Galaxies, they are still two separate spiral galaxies. They are only in the first step of colliding and merging. Soon they will collide, probably looking a bit more like the Mice Galaxies. In about a billion years time they are expected to merge and become an elliptical galaxy or perhaps a disk galaxy.

12.Pinwheel Galaxy



The Pinwheel Galaxy (also known as Messier 101, M101 or NGC 5457) is a face-on spiral galaxy distanced 21 million light-years (six megaparsecs) away from earth in the constellation Ursa Major. First discovered by Pierre Méchain on March 27, 1781, it was communicated to Charles Messier who verified its position for inclusion in the Messier Catalogue as one of its final entries. On February 28, 2006, NASA and the European Space Agency released a very detailed image of the Pinwheel Galaxy, which was the largest and most detailed image of a galaxy by Hubble Space Telescope at the time.The image was composed from 51 individual exposures, plus some extra ground-based photos. On August 24, 2011, a Type Ia supernova, SN 2011fe, was discovered in M101.

13.Sombrero Galaxy



Sombrero Galaxy' (also known as Messier Object 104, M104 or NGC 4594) is an unbarred spiral galaxy in the constellationVirgo located 31 million light-years (9.55 Mpc) from Earth. The galaxy has a diameter of approximately 50,000 light-years, 30% the size of the Milky Way. It has a bright nucleus, an unusually large central bulge, and a prominent dust lane in its inclined disk. The dark dust lane and the bulge give this galaxy the appearance of a sombrero. Astronomers initially thought that the halo was small and light, indicative of a spiral galaxy, but Spitzer found that the halo around the Sombrero Galaxy is larger and more massive than previously thought, indicative of a giant elliptical galaxy. The galaxy has an apparent magnitude of +9.0, making it easily visible with amateur telescopes, and it is considered by some authors to be the brightest galaxy within a radius of 10 megaparsecs of the Milky Way. The large bulge, the central supermassive black hole, and the dust lane all attract the attention of professional astronomers.



14.Tadpole Galaxy


The Tadpole Galaxy recorded with the Hubble Space Telescope's Advanced Camera for Surveys.

The Tadpole Galaxy is a disrupted barred spiral galaxy located 420 million light-years from Earth toward the northernconstellation Draco. Its most dramatic features are a trail of stars about 280,000 light-years long and massive, bright blue star clusters.

It is hypothesized that a more compact intruder galaxy crossed in front of the Tadpole Galaxy—from left to right from the perspective of Earth—and was slung around behind the Tadpole by their mutual gravitational attraction. During this close encounter, tidal forces drew out the spiral galaxy's stars, gas, and dust, forming the conspicuous tail.

15.Whirlpool Galaxy

The Whirlpool Galaxy, also known as Messier 51a, M51a, or NGC 5194, is an interacting grand-design spiral galaxy with aSeyfert 2 active galactic nucleus in the constellation Canes Venatici. It was the first galaxy to be classified as a spiral galaxy.Recently it was estimated to be 23 ± 4 million light-years from the Milky Way, but different methods yield distances between 15 and 35 million light-years. Messier 51 is one of the best known galaxies in the sky.


16. Mice Galaxies





NGC 4676, or the Mice Galaxies, are two spiral galaxies in the constellation Coma Berenices. About 290 million light-years away, they began the process of colliding and merging about 290 million years ago. Their name refers to the long tails produced by tidal action—the relative difference between gravitational pulls on the near and far parts of each galaxy—known here as a galactic tide. Members of the Coma cluster, it is a possibility that both galaxies have experienced collision, and will continue colliding until they coalesce.

The colors of the galaxy are peculiar. In the upper galaxy (NGC 4676A, to the right in the photo), a core with some dark markings is surrounded by a bluish white remnant of spiral arms. The tail is unusual, starting out blue and terminating in a more yellowish color, despite the fact that the beginning of each arm in virtually every spiral galaxy starts yellow and terminates in a bluish color. The lower galaxy (NGC 4676B, to the left) is closer to normal, with a yellowish core and two arcs; arm remnants underneath are bluish as well.The galaxies were photographed in 2002 by the Hubble Space Telescope.



17.NGC 2207 and IC 2163



NGC 2207 and IC 2163 are a pair of colliding spiral galaxies about 80 million light-years away in the constellation Canis Major. Both galaxies were discovered by John Herschel in 1835. The larger spiral, NGC 2207, is classified as an intermediate spiral galaxy exhibiting a weak inner ring structure around the central bar. The smaller companion spiral, IC 2163, is classified as a barred spiral galaxy that also exhibits a weak inner ring and an elongated spiral arm that is likely being stretched by tidal forces with the larger companion. Both galaxies contain a vast amount of dust and gas, and are beginning to exhibit enhanced rates of star formation, as seen in infrared images. So far, four supernovae have been observed in NGC 2207.NGC 2207 is in the process of colliding and merging with IC 2163. But unlike the Antennae or the Mice Galaxies, they are still two separate spiral galaxies. They are only in the first step of colliding and merging. Soon they will collide, probably looking a bit more like the Mice Galaxies. In about a billion years time they are expected to merge and become an elliptical galaxy or perhaps a disk galaxy.


18.Butterfly Galaxies

NGC 4567 and NGC 4568 (nicknamed the Siamese Twins or the Butterfly Galaxies) are a set of unbarred spiral galaxiesabout 60 million light-years away in the constellation Virgo. They were both discovered by William Herschel in 1784. They are part of the Virgo cluster of galaxies. Only one supernova (SN 2004cc) has been observed in the Siamese Twins.

These galaxies are in the process of colliding and merging with each other, as studies of their distributions of neutral and molecular hydrogen show, with the highest star formation activity in the part where they overlap. However the system is still in an early phase of interaction.

They were named "Siamese Twins" because they appear to be connected.





"It boggles the mind that over 90 percent of the galaxies in the Universe have yet to be studied. Who knows what interesting properties we will find when we discover these galaxies with future generations of telescopes?" said Christopher Conselice, a Professor of astrophysics at the University of Nottingham, who led the study peering into the depths of the early Universe.

For the study, astronomers trawled through images captured by the Hubble Space Telescope and other observatories to examine the galaxies of the early Universe. As the Universe has aged, small galaxies have merged to create larger galaxies, leading the overall population of galaxies to drop as time goes. This study provides strong evidence to prove the assumption that the early universe had many more galaxies than our present-day Universe.

"These results are powerful evidence that a significant galaxy evolution has taken place throughout the Universe's history, which dramatically reduced the number of galaxies through mergers between them — thus reducing their total number. This gives us a verification of the so-called top-down formation of structure in the Universe," explained Conselice.


In 1995, the Hubble Deep Field experiment imaged a small section of the constellation Ursa Major in order to estimate the number of galaxies in the Universe. In-depth analysis of the faint smudges captured by Hubble led astronomers to estimate that the observable universe contains about 200 billion galaxies. That number is now thought to be just a tenth of the real number of galaxies in the Universe.

Conselice and his team took images from Hubble and recreated them in 3D in order to measure the number of galaxies at different points in the Universe’s past. The team also developed new mathematical models which let them infer the existence of galaxies that current telescopes cannot see. Those models led the team to conclude that, in order for the number and mass of current galaxies to match up, 90 per cent of galaxies in the observable Universe must be too dim or far away to be studied.

"In the near future, the James Webb Space Telescope will be able to study these ultra-faint galaxies," said Conselice.

The James Webb Space Telescope will succeed the Hubble Space Telescope as the most advanced observatory operated by humans. Unlike Hubble, which is in orbit around the Earth, the JWST will orbit the Sun and point its 6.5-metre primary mirror deep into space to observe the earliest parts of the Universe ever seen. Built in collaboration between Nasa, the European Space Agency and the Canadian Space Agency, the telescope is due to be launched from French Guiana in October 2018.

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