Dwarf galaxies may be very small, but they have a phenomenal power that can give birth to new stars. New observations from the Hubble Space Telescope show that star formation in dwarf galaxies plays a larger role in the early universe than is currently believed.
And although galaxies throughout the universe are still forming new stars, most of them were formed between two and six billion years after the Big Bang. Studying this early era of the universe's history is key if we are to understand how the first stars appeared and how the first galaxies grew and evolved.
This image shows a patch of sky marked with dwarf galaxies that are experiencing bursts of star formation. The image was taken as part of the GOODS (Great Observatories Origins Deep Survey) program and shows only one frame from the entire survey. Source: NASA, ESA, the GOODS Team and M. Giavalisco (STScI/University of Massachusetts)
A new study using Hubble's Wide Field Camera 3 (WFC3) has allowed astronomers to take a step forward in understanding the era by examining different types of dwarf galaxies in the early universe and, in particular, selecting only those with obvious star formation processes. . Such galaxies are usually called starburst galaxies. In such objects, new stars form much faster than usual in other galaxies. Previous studies have focused primarily on medium- and high-mass galaxies and have not taken into account the huge number of dwarf galaxies that existed during this active era. But the fault here lies not so much with the scientists who did not want to explore dwarf galaxies. This is most likely due to the inability to see these small objects, since they are very far away from us. Until recently, astronomers could observe small galaxies at smaller distances or large galaxies at greater distances.
However, now, using grism, astronomers have been able to peer at low-mass dwarf galaxies in the distant universe and take into account the contribution of their star formation bursts, approximating the information to the possible number of small galaxies that then existed. A grism is an objective prism, a combination of a prism and a diffraction grating, which transmits light without shifting its spectrum. The letter “G” in the name comes from grating.
“We've always assumed that starburst dwarf galaxies would have a significant effect on new star formation in the young universe, but this is the first time we've been able to measure the effect they actually have. And, apparently, they played a significant, if not key role,” Hakim Atek from the Swiss Polytechnic University.
“These galaxies form stars so quickly that they could actually double their entire stellar mass in just 150 million years. By comparison, stellar masses for ordinary galaxies double on average every 1-3 billion years,” adds co-author Jean-Paul Kneib.
An image of galaxies in grism mode using the example of the Wide Field Camera 3 installed on Hubble and operating in this spectroscopy mode. Extended rainbow lines are nothing more than galaxies caught in the lens, but in grism mode they are presented as a rainbow spectrum. Thanks to this, scientists are able to assess the chemical composition of space objects.
Any star is a huge ball of gas, which consists of helium and hydrogen, as well as traces of other chemical elements. There are a huge number of stars and they all differ in size and temperature, and some of them consist of two or more stars that are connected by gravity. From Earth, some stars are visible to the naked eye, while others can only be seen through a telescope. However, even with special equipment, not every star can be viewed the way you want, and even in powerful telescopes, some stars will look like nothing more than just luminous points.
Thus, an ordinary person with fairly good visual acuity, in clear weather in the night sky, can see about 3000 stars from one earthly hemisphere, however, in fact, there are much more of them in the Galaxy. All stars are classified according to size, color, temperature. Thus, there are dwarfs, giants and supergiants.
Dwarf stars are of the following types:
- yellow dwarf. This type is a small main sequence star of spectral class G. Their mass ranges from 0.8 to 1.2 solar masses.
- orange dwarf. This type includes small main sequence stars of spectral class K. Their mass is 0.5 - 0.8 solar masses. Unlike yellow dwarfs, orange dwarfs have longer lifespans.
- red dwarf. This type unites small and relatively cool main sequence stars of spectral class M. Their differences from other stars are quite pronounced. They have a diameter and mass that is no more than 1/3 of the Solar one.
- blue dwarf This type of star is hypothetical. Blue dwarfs evolve from red dwarfs before burning out all their hydrogen, after which they presumably evolve into white dwarfs.
- white dwarf. This is a type of already evolved stars. They have a mass that is not more than the mass of Chandrasekhar. White dwarfs do not have their own source of thermonuclear energy. They belong to the spectral class DA.
- black dwarf. This type is a cooled white dwarf, which, accordingly, does not emit energy, i.e. do not glow, or emit it very, very weakly. They represent the final stage of the evolution of white dwarfs in the absence of accretion. The mass of black dwarfs, like white dwarfs, does not exceed the mass of Chandrasekhar.
- brown dwarf. These stars are substellar objects that have a mass from 12.57 to 80.35 Jupiter masses, which, in turn, corresponds to 0.012 - 0.0767 solar masses. Brown dwarfs differ from main sequence stars in that the thermonuclear fusion reaction that converts hydrogen into helium in other stars does not occur in their cores.
- subbrown dwarfs or brown subdwarfs. They are absolutely cold formations, the mass of which is below the limit of brown dwarfs. To a greater extent, they are considered to be planets.
So, it can be noted that stars classified as white dwarfs are those stars that are initially small in size and are at their final stage of evolution. The history of the discovery of white dwarfs goes back to the relatively recent year 1844. It was at that time that the German astronomer and mathematician Friedrich Bessel, while observing Sirius, discovered a slight deviation of the star from linear motion. As a result of this, Friedrich suggested that Sirius had an invisible massive companion star. This assumption was confirmed in 1862 by the American astronomer and telescope builder Alvan Graham Clark during the adjustment of the largest refractor at that time. A dim star was discovered near Sirius, which was later named Sirius B. This star is characterized by low luminosity, and its gravitational field affects its bright partner quite noticeably. This, in turn, confirms that this star has a very small radius with a significant mass.
Which stars are dwarfs
Dwarfs are evolved stars that have a mass that does not exceed the Chandrasekhar limit. The formation of a white dwarf occurs as a result of the burning of all hydrogen. When hydrogen burns out, the core of the star contracts to high densities, while at the same time the outer layers expand greatly and are accompanied by a general dimming of luminosity. Thus, the star first turns into a red giant, which sheds its shell. The shedding of the shell occurs due to the fact that the outer layers of the star have an extremely weak connection with the central hot and very dense core. Subsequently, this shell becomes an expanding planetary nebula. It is worth paying attention to the fact that red giants and white dwarfs have a very close relationship.
All white dwarfs are divided into two spectral groups. The first group includes dwarfs that have the “hydrogen” spectral class DA, in which there are no spectral lines of helium. This type is the most common. The second type of white dwarf is DB. It is rarer and is called a helium white dwarf. No hydrogen lines were detected in the spectrum of stars of this type.
According to the American astronomer Iko Iben, these types of white dwarfs are formed in completely different ways. This is due to the fact that helium combustion in red giants is unstable and the development of layered helium flares periodically occurs. Iko Iben also suggested a mechanism by which the shell is shed at different stages of the development of a helium flash - at its peak and between flashes. Accordingly, its formation is influenced by the membrane shedding mechanism.
Messier 32, or M32, is a type of dwarf galaxy with an elliptical shape. Located in the constellation Andromeda. M32 has an apparent magnitude of 8.1 with an angular size of 8 x 6 arcminutes. The galaxy is 2.9 million light years away from our planet. According to Equinox 2000, the following coordinates are derived: right ascension 0 hours 42.8 minutes; declination +40 ° 52′. Thanks to this, the galaxy can be seen throughout the fall.
Messier 32 refers to the two elliptical satellite galaxies of Andromeda Magna that can be seen in the provided images. Along the lower edge of object M31, galaxy M32 is the closest galaxy, while object M110 is the most distant galaxy along the upper right edge. M31 is a large Andromeda galaxy, represented by a bright celestial object that can be observed with the naked eye. Messier 31, Messier 32 and Messier 110 belong to the Local Group of galaxies. It also includes the Triangulum Galaxy and the Milky Way.
The images provided show uncompressed photographs of all three objects - M31, M32 and M110. All photos were taken using a Takahashi E-180 astrograph. Nearby is a 3x magnification image of the center of the Messier 32 galaxy.
The object was included in Messier's catalog, but was discovered by the French scientist Le Gentil in 1749. Based on data from advanced researchers in 2010, it is possible to calculate approximate data for this galaxy. The distance from Earth to Messier 32 is 2.57 million light-years, the approximate mass varies between 300,000,000 solar masses, and its diameter reaches 6,500 light-years.
Observations
M32 is a small galaxy, but has a bright elliptical shape. When amateurs look at the Andromeda Nebula, this particular object will seem strange to them. Even the most ordinary telescope will reveal the features of the diffuse nature of the galaxy. It is located half a degree south of the center of the M31 galaxy. If you look at M32 with a medium-quality telescope, you can see a star-shaped core and a compact oval halo that gradually decreases in brightness.
Nearby objects from the Messier catalog
The first neighbor of the M32 galaxy is its physical satellite, the Andromeda Nebula. This is a spiral supergiant galaxy. The second neighboring galaxy is the elliptical M110, and the third is M31, a satellite that is on the other side of Messier 32.
Thanks to the Dwarf Galaxy, you can see the globular cluster G156. It belongs to object M31. The best instrument for observation is a telescope with an aperture of 400 mm.
Description of Messier 32 in the catalog
August 1764
Below Andromeda's belt for a few minutes there is a small starless nebula. Compared to the belt, this small nebula has a dimmer light. It was discovered by Le Gentil on October 29, 1749, and in 1757 it was seen by Messier.
Technical details of the photograph of Messier 32
Object: M32
Other designations: NGC 221
Object type: Dwarf elliptical galaxy
Position: Bifrost Astronomical Observatory
Mount: Astro-Physics 1200GTO
Telescope: Hyperbolic astrograph TakahashiEpsilon 180
Camera: Canon EOS 550D (Rebel T2i) (Baader UV/IR filter)
Exposure: 8 x 300s, f/2.8, ISO 800
Original photo size: 3454 × 5179 pixels (17.9 MP); 11.5″ x 17.3″ @ 300 dpi
The image shows the Dwarf Galaxy in the constellation Sculptor Dwarf Galaxy. The image was taken by the Wide Field Imager, which is installed on the 2.2-meter MPG/ESO telescope at the European Southern Observatory in La Silla. This galaxy is one of the neighbors of our Milky Way. But, despite such close proximity to each other, these two galaxies have completely different histories of origin and evolution; one can say that their characters are completely different. The Sculptor dwarf galaxy is much smaller and older than the Milky Way, making it a very valuable object for studying the processes that led to the birth of new stars and other galaxies in the early Universe. However, due to the fact that it emits very little light, its study is very difficult.
The dwarf galaxy in the constellation Sculptor belongs to the subclass of dwarf spheroidal galaxies and is one of fourteen satellite galaxies that orbit the Milky Way. They are all located close to each other in the halo region of our Galaxy, which is a spherical region extending far beyond the boundaries of the spiral arms. As its name suggests, this dwarf galaxy is located in the constellation Sculptor and lies at a distance of 280,000 light years from Earth. Despite its proximity, it was only discovered in 1937 with the advent of new powerful instruments, since its component stars are very faint and seem to be scattered throughout the sky. Also, do not confuse this galaxy with NGC 253, which is located in the same constellation Sculptor, but looks much brighter and is a barred spiral.
Dwarf galaxy in the constellation Sculptor. Source: ESO
Photo information
Photo information
Although difficult to detect, this dwarf galaxy was among the first faint dwarf objects discovered in the region around the Milky Way. Its strange shape has given astronomers pause since its discovery to this day. But in our time, astronomers have become accustomed to spheroidal galaxies and have realized that such objects allow us to look far into the past of the Universe.
It is believed that the Milky Way, like all large galaxies, was formed as a result of mergers with smaller objects during the early years of the Universe. And if some of these small galaxies still exist today, then they must contain many extremely old stars. That is why the Dwarf Galaxy in the constellation Sculptor meets all the requirements that apply to primordial galaxies. It is these ancient stars that can be observed in this image.
Astronomers have learned to determine the age of stars in a galaxy by the characteristic signatures that are present in their light flux. This radiation carries very little evidence of the presence of heavy chemical elements in these objects. The fact is that such chemical compounds tend to accumulate in galaxies as generations of stars change. Thus, low concentrations of heavy molecules indicate that the average age of stars in this spheroidal galaxy is quite high.
The area of sky around the dwarf galaxy in the constellation Sculptor.
The scientists' study shows how widespread this type of star actually is in our galaxy and how actively they take part in the formation of new stars.
The figures show that 2 -3 stars of other classes account for at least 1 brown dwarf.
This type of space objects clearly stands out from the rest.
They are too big and hot (in 15 -80 times more massive than our Jupiter) so that they can be classified as planets, but at the same time they are too small to be full-fledged stars - they do not have enough mass to maintain stable hydrogen fusion in the core.
However, brown dwarfs initially form in the same way as normal stars, which is why they are often called failed stars.
More in 2013 year, astronomers began to suspect that brown dwarfs are quite common in our galaxy, calculating the approximate number of them in the region 70 billion
However, new data presented at the National Astronomy conference M eeting, held recently at the English University of Hull, they say that there may be about 100 billion
Considering that the entire Milky Way can contain, according to rough estimates, up to 400 billions of stars, the number of brown dwarfs is both impressive and disappointing.
To clarify the results, astronomers conducted a study of more than a thousand brown dwarfs located within a radius of no more than 1500 light years. Since stars of this class are very dim, observing them at longer distances seems extremely difficult, if not impossible.
Most of the brown dwarfs we know of were found in regions where new stars are forming, known as clusters.
One of these clusters is the object NG C133 , which contains almost as many brown dwarfs as ordinary stars.
This seemed quite strange to Alex Scholz from the University of St Andrews and his colleague Koralka Muzic from the University of Lisbon. To gain a more detailed understanding of the frequency of brown dwarfs born within star clusters of varying densities, the researchers decided to look for more distant dwarfs in the denser star cluster R C W 38 .
To be able to view a distant cluster located approximately 5000 light years away, astronomers used the NA camera C O with adaptive optics mounted on the European Southern Observatory's Very Large Telescope.
As in previous observations, this time scientists also discovered that the number of brown dwarfs in this cluster is almost half of the total number of stars in it, which, in turn, suggests that the frequency of birth of brown dwarfs does not depend at all on the star itself. composition of star clusters.
“...We discovered a large number of brown dwarfs in these clusters. It turns out that regardless of the type of cluster, this class of stars is found quite often. And since brown dwarfs form together with other stars in clusters, we can conclude that there really are a lot of them in our galaxy..."
- comments Scholz.
It could be a number in 100 billion However, there may be even more of them.
Let us remember that brown dwarfs are very dim stellar objects, so their even fainter representatives could simply not fall into the field of view of astronomers.
At the time of this writing, the results of Scholz's latest research were awaiting critical review by outside scientists, but the first comments on these observations to Gizmodo came from astronomer John Omira of the College of Saint Miguel, who was not involved in the work, but believes that the figures reflected in it may be are true.
"...They come to the number 100 billions, making a lot of assumptions for this. But in fact, the conclusion about the number of brown dwarfs in a star cluster is based on the so-called initial mass function, which describes the distribution of masses of stars in the cluster. Once you know this function and you know the frequency with which the galaxy forms stars, then you can calculate the number of stars of a certain type. Therefore, if we omit a couple of assumptions, then the figure in 100 billions really seems real..."
- Omira commented.
And by comparing the number of brown dwarfs in two different clusters - one with a dense and one with a less dense distribution of stars - the researchers showed that the environment in which stars appear is not always the key factor regulating the frequency of occurrence of this type of stellar object.
“The formation of brown dwarfs is a universal and integral part of star formation in general.”, says Omira.
Professor Abel Mendez from the Planetary Habitability Laboratory L aboratory, another astronomer who also did not take part in the study under discussion, says that the numbers in the new work may actually make sense, especially considering the fact that our galaxy contains significantly more compact stellar objects than larger ones.
“...Small red dwarfs, for example, are much more common than all other types of stars. Therefore, I would suggest that the new numbers are more likely even the lower limit..."
says Mendez.
There is, of course, a downside to the prolific nature of brown dwarfs. A large number of failed stars also means a decrease in habitability potential.
Mendez says brown dwarfs are not stable enough to support an environment called the habitable zone. In addition, not all astronomers like the term itself “failed stars”.
“...Personally, I prefer not to call brown dwarfs “failed stars”, since, in my opinion, they simply do not deserve the title of stars...”
— comments Jacqueline Faherty, astrophysicist at the American Museum of Natural History.
“... I would rather call them “overgrown planets”, or simply “superplanets”, since from the point of view of their masses they are still closer to these astronomical objects than to stars...”
- says the scientist.
