Astronomy

Which galaxy is closest to the center of the KBC void?

Which galaxy is closest to the center of the KBC void?


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I was reading up on Bootes void and came across this list of the largest voids in the visible universe, and apparently the one we're in, the KBC void, is not only the biggest, but damned-near spherical. The Wikipedia page says that the Milky Way is within a few hundred million light-years of the center of the KBC void, but I'm unable to find out what, if anything, is closest to the center.

Is this information available anywhere? Does anyone know what's at the center of the KBC void?


In Our Skies: Out into the void and super void

Ever since the invention of the telescope in the early 17th century, the study of astronomy has been to a large degree a continuous exercise in showing us just how large and immense is the universe within which we live – and, alongside this, the corresponding smallness and relative insignificance of our own world.

The realization that the stars that populate the nighttime sky are objects like our own sun, but viewed from immense distances, took a while to seep into our collective consciousness, but when the first distance measurement to another star was performed by the German astronomer Friedrich Bessel in 1838 of the star 61 Cygni located in the eastern wing of the constellation Cygnus, the swan, now located in our northwestern sky after dusk, this proved to be much greater than anyone expected.

61 Cygni, as it turns out, is located 11.4 light-years away from us – where one light-year, defined as the distance light travels in one year, is slightly under six trillion miles – thus its distance is 67 trillion miles. And 61 Cygni is actually one of the closest stars to our solar system . . .

A century ago one of the biggest questions in astronomy was whether or not our galaxy – comprising all the stars visible in the nighttime sky, including the distant stars that make up the hazy band of light we call the Milky Way that this time of year stretches from our western sky up over to our north – is the only such structure in the universe, or if ours is just one of many galaxies in the universe.

This question was answered in the mid-1920s by American astronomer Edwin Hubble, who conclusively demonstrated that the hazy Andromeda Nebula – now in our northeastern sky during the evening hours, and visible to the unaided eye from dark rural sites – is so far away that it has to be a separate galaxy. The Andromeda Galaxy, as we now call it, is located 2.5 million light-years from us.

The number of galaxies in the universe is now known to be in the hundreds of billions – roughly comparable to the number of stars in our own galaxy. Rather than being distributed randomly throughout the universe, we’ve found that galaxies tend to congregate in clusters, which can include anywhere from a handful of galaxies up to several thousand.

Our own such cluster, which has been dubbed the Local Group, is relatively small, and includes our galaxy together with some smaller satellite galaxies, including the two bright Magellanic Clouds visible from the southern hemisphere, the Andromeda Galaxy, a handful of medium-sized galaxies, and a few dozen rather tiny ones.

The nearest large cluster, located in the constellation Virgo now visible low in our eastern sky before dawn, is some 60 million light-years away and contains a couple of thousand galaxies.

These galaxy clusters are also not randomly distributed throughout the universe, but instead congregate into even larger structures dubbed superclusters.

Our understanding of this continues to evolve, and just a few years ago astronomers recognized that we are part of such a supercluster that has been named Laniakea, from Hawaiian words meaning immense heaven, that stretches across 500 million light-years and that contains up to 500 clusters, including the Local Group and the large cluster in Virgo, collectively containing up to 100,000 galaxies.

Even these superclusters are not randomly distributed throughout the universe. Beginning in the late 1970s astronomers realized that these structures are arranged in long filaments and walls, between which are largely empty regions of space known as voids. These may extend several hundred million light-years and at most contain just a few isolated galaxies.

The nearest such void is known as the Local Void, or sometimes as the Tully Void after University of Hawaii astronomer Brent Tully, who co-discovered it, along with fellow American astronomer Rick Fisher, in 1987. The Local Void, which is centered in the constellation Aquila now in our western sky after dusk, begins just beyond the Local Group and extends – in a direction perpendicular to that towards the Virgo Cluster – up to 250 million light-years. Only a handful of mostly isolated galaxies have been found within the Local Void.

Many other such voids have been found throughout the universe. Quite a few of these are significantly larger than the Local Void, and some are so large – up to one to two billion light-years across – that the term super void has been used to describe them. The largest known such structure, known as the KBC Void after astronomers Ryan Keenan, Amy Barger, and Lennox Cowie who inferred its existence five years ago, appears to be two billion light-years across and completely enshrouds the Laniakea Supercluster and several other superclusters, all of which are mere filaments within an otherwise mostly empty volume of space.

The universe is not static, but rather is quite dynamic, although usually along very long timescales. While the overall universe continues to expand, the structures of superclusters and voids makes this bumpy rather than smooth.

For example, our galaxy is being gravitationally pulled towards the Virgo Cluster and is being pushed away from the Local Void. It’ll be billions of years before there are any significant apparent changes, and meanwhile in a similar timeframe our galaxy and the Andromeda Galaxy, which are moving towards each other, will have collided and merged into one very large galaxy.

The sun will undergo its own changes during this time and thus Earth may no longer exist by then . . . but in any event, time and space continue on as always.

Alan Hale is a professional astronomer who resides in Cloudcroft. Hale is involved in various space-related research and educational activities throughout New Mexico and elsewhere.


Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2008 January 10
Active Galaxy Centaurus A
Credit: X-ray - NASA, CXC, R.Kraft (CfA), et al.
Radio - NSF, VLA, M.Hardcastle (U Hertfordshire) et al. Optical - ESO, M.Rejkuba (ESO-Garching) et al.

Explanation: A mere 11 million light-years away, Centaurus A is a giant elliptical galaxy - the closest active galaxy to Earth. This remarkable composite view of the galaxy combines image data from the x-ray ( Chandra), optical(ESO), and radio(VLA) regimes. Centaurus A's central region is a jumble of gas, dust, and stars in optical light, but both radio and x-ray telescopes trace a remarkable jet of high-energy particles streaming from the galaxy's core. The cosmic particle accelerator's power source is a black hole with about 10 million times the mass of the Sun coincident with the x-ray bright spot at the galaxy's center. Blasting out from the active galactic nucleus toward the upper left, the energetic jet extends about 13,000 light-years. A shorter jet extends from the nucleus in the opposite direction. Other x-ray bright spots in the field are binary star systems with neutron stars or stellar mass black holes. Active galaxy Centaurus A is likely the result of a merger with a spiral galaxy some 100 million years ago.


We're Way Below Average! Astronomers Say Milky Way Resides In A Great Cosmic Void

Outlined in light blue, giant collections of galaxies can be divided up into superclusters. But our . [+] supercluster, along with many nearby ones, might still reside in an even larger cosmic void.

R. Brent Tully, Hélène Courtois, Yehuda Hoffman & Daniel Pomarède, Nature 513, 71–73 (04 September 2014)

If you went to give our cosmic address, you might tell someone that we lived on planet Earth, orbiting our Sun, on the outskirts of a spur of the Milky Way's spiral arms, in the second largest galaxy in our local group, about 50 million light years from the Virgo Cluster, embedded within the Laniakea supercluster. Well, you might have to add another line to that address, as Laniakia, along with dozens of other nearby giant clusters, is all embedded within a great cosmic void stretching a billion light years from end-to-end. This below-average region of space is consistent with everything we observe, supported by new observations presented at this week's American Astronomical Society meeting, and just might provide the solution to one of the Universe's greatest discrepancies.

The simulated large-scale structure of the Universe shows intricate patterns of clustering that . [+] never repeat. But from our perspective, we can only see a finite volume of the Universe, which appears uniform on the largest scales.

V. Springel et al., MPA Garching, and the Millenium Simulation

On the largest scales, the Universe is uniform, with equal amounts of matter and energy everywhere. If you drew an imaginary sphere a few billion light years wide around any point and measured the total amount of mass inside, you'd get the same number everywhere, to about 99.99% accuracy. But if your sphere were smaller, you'd see you'd start to get different numbers in different locations. Gravitation pulls matter into filaments, groups and clusters of galaxies, and steals matter away from less dense regions, creating great cosmic voids.

A map of the local universe as observed by the Sloan Digital Sky Survey. The orange areas have . [+] higher densities of galaxy clusters and filaments.

Today, matter in the Universe is distributed like a combination of a spider web and swiss cheese. The "holes" in the Universe are stupendous, with some stretching tens of millions of light years across before you run into any galaxies at all. On the other hand, there are places where filaments intersect — a great nexus in the cosmic web — that correspond to the locations and existences of ultra-large galaxy clusters, some of which contain many thousands of times the mass of our galaxy.

The Universe contains many overdense and underdense regions of varying sizes, but appears smooth if . [+] you zoom out far enough.

Andrew Z. Colvin of Wikimedia Commons

But in between scales where there are huge density differences and those where the density averages out to the same number every time, something interesting is happening. On scales ranging from about half a billion to three billion light years in diameter, you might find that two different regions that look very similar on the surface — containing voids and clusters, filaments lined with galaxies, multiple "swiss cheese" holes, etc. — might actually differ in their overall densities by about 20% or more. Without doing a very large, detailed survey of a very large set of regions in the Universe (e.g., going well beyond billions of light years), you'd have no way to know for certain whether you lived in one or not.

The construction of the cosmic distance ladder involves going from our Solar System to the stars to . [+] nearby galaxies to distant ones. Each “step” carries along its own uncertainties it also would be biased towards higher or lower values if we lived in an underdense or overdense region.

NASA,ESA, A. Feild (STScI), and A. Riess (STScI/JHU)

But there would be a hint. If you lived in an overdense region, even one that looked very much like an average region in every other respect, you'd find that there would be one thing that looked weird: the expanding Universe. Because you had more matter than average where you were, the galaxies nearby would mutually gravitate more forcefully, and the expansion rate of the Universe would appear slower for you. If you looked to very large, distant scales, the expansion rate would appear normal again, but right where you are, you'd measure it to be lower-than-average. Any technique that only relied on nearby measurements — things like parallax, cepheids, or even most supernovae — would give you that skewed result.

Modern measurement tensions from the distance ladder (red) with CMB (green) and BAO (blue) data.

On the other hand, if you lived in an underdense region, your local neighborhood of space would gravitate less strongly than average, and the expansion rate would appear greater (higher) for you. We've noticed this exact problem in our measurements for a few years now: if we try and measure the expansion rate using these cosmic distance ladder techniques, we find that the Universe expands about 5-10% more quickly than other methods indicate. If we use data from the cosmic microwave background or from the large-scale clustering of the Universe, we get a value for the Hubble expansion rate of 67-68 km/s/Mpc, while relatively nearby galaxies show a rate that's more like 72-75 km/s/Mpc.

Three different types of measurements, distant stars and galaxies, the large scale structure of the . [+] Universe, and the fluctuations in the CMB, tell us the expansion history of the Universe.

NASA/ESA Hubble (top L), SDSS (top R), ESA and the Planck Collaboration (bottom)

According to research carried out by Amy Barger's team at University of Wisconsin-Madison, the void that contains our Milky Way is huge, spherical, and contains not only our own local supercluster but many superclusters beyond that. Although simulations predict voids ranging from tens of millions of light years up to a few billion, our measurements haven't gotten good enough to measure the largest voids precisely. With a radius of roughly one billion light years, the void containing our Milky Way, known as the KBC void (for scientists Keenan, Barger, and Cowie), is the largest confirmed void in the Universe.

Over time, gravitational interactions will turn a mostly uniform, equal-density Universe into one . [+] with large concentrations of matter and huge voids separating them.

According to new research presented by Ben Hoscheit at this week's American Astronomical Society meeting, this void is entirely consistent with being large, spherical, and containing the Milky Way within a few hundred million light years of its center. Amy Barger put this new confirmation in context:

"It is often really hard to find consistent solutions between many different observations. What Ben has shown is that the density profile that Keenan measured is consistent with cosmological observables. One always wants to find consistency, or else there is a problem somewhere that needs to be resolved."

A region of space devoid of matter in our galaxy reveals the Universe beyond, where every point is a . [+] distant galaxy. The cluster/void structure can be seen very clearly.

If there weren't a large cosmic void that our Milky Way resided in, this tension between different ways of measuring the Hubble expansion rate would pose a big problem. Either there would be a systematic error affecting one of the methods of measuring it, or the Universe's dark energy properties could be changing with time. But right now, all signs are pointing to a simple cosmic explanation that would resolve it all: we're simply a bit below average when it comes to density.


“Obscured” –Vast Void Behind Center of the Milky Way

The universe is a tapestry of galaxy congregations and vast voids. In a new study applies the same tools from an earlier study to map the size and shape of an extensive empty region they called the Local Void that borders the Milky Way that has remained poorly studied because it lies behind the center of our galaxy and is heavily obscured from our view.

Using the observations of galaxy motions, reported in The Astrophysical Journal, Brent Tully‘s team at the University of Hawaii infer the distribution of mass responsible for that motion, and constructed three-dimensional maps that reveal more of the vast cosmic structure surrounding our Milky Way galaxy.

A smoothed rendition of the structure surrounding the Local Void is shown below. The Milky Way galaxy lies at the origin of the red-green-blue orientation arrows (each 200 million lightyears in length). It is at a boundary between a large, low density void, and the high density Virgo cluster.

Galaxies not only move with the overall expansion of the universe, they also respond to the gravitational tug of their neighbors and regions with a lot of mass. As a consequence, relative to the overall expansion they are moving towards the densest areas and away from regions with little mass – the voids.

Although we live in a cosmic metropolis, back in 1987 Tully and Richard Fisher noted that our Milky Way galaxy is also at the edge of an extensive empty region that they called the Local Void.

Now, Tully and his team have measured the motions of 18,000 galaxies in the Cosmicflows-3 compendium of galaxy distances, constructing a cosmographic map that highlights the boundary between the collection of matter and the absence of matter that defines the edge of the Local Void. They used the same technique in 2014 to identify the full extent of our home supercluster of over one hundred thousand galaxies, giving it the name Laniakea, meaning “immense heaven” in Hawaiian.

For 30 years, astronomers have been trying to identify why the motions of the Milky Way, our nearest large galaxy neighbor Andromeda, and their smaller neighbors deviate from the overall expansion of the Universe by over 600 km/s (1.3 million mph). The new study shows that roughly half of this motion is generated “locally” from the combination of a pull from the massive nearby Virgo Cluster and our participation in the expansion of the Local Void as it becomes ever emptier.


Astronomers map vast void in our cosmic neighborhood

A smoothed rendition of the structure surrounding the Local Void. Our Milky Way galaxy lies at the origin of the red-green-blue orientation arrows (each 200 million lightyears in length). We are at a boundary between a large, low density void, and the high density Virgo cluster. Credit: R. Brent Tully

An astronomer from the University of Hawaiʻi Institute for Astronomy (IfA) and an international team published a new study that reveals more of the vast cosmic structure surrounding our Milky Way galaxy.

The universe is a tapestry of galaxy congregations and vast voids. In a new study being reported in The Astrophysical Journal, Brent Tully's team applies the same tools from an earlier study to map the size and shape of an extensive empty region they called the Local Void that borders the Milky Way galaxy. Using the observations of galaxy motions, they infer the distribution of mass responsible for that motion, and construct three-dimensional maps of our local Universe.

Galaxies not only move with the overall expansion of the universe, they also respond to the gravitational tug of their neighbors and regions with a lot of mass. As a consequence, they are moving towards the densest areas and away from regions with little mass—the voids.

Although we live in a cosmic metropolis, back in 1987 Tully and Richard Fisher noted that our Milky Way galaxy is also at the edge of an extensive empty region that they called the Local Void. The existence of the Local Void has been widely accepted, but it remained poorly studied because it lies behind the center of our galaxy and is therefore heavily obscured from our view.

Now, Tully and his team have measured the motions of 18,000 galaxies in the Cosmicflows-3 compendium of galaxy distances, constructing a cosmographic map that highlights the boundary between the collection of matter and the absence of matter that defines the edge of the Local Void. They used the same technique in 2014 to identify the full extent of our home supercluster of over one hundred thousand galaxies, giving it the name Laniakea, meaning "immense heaven" in Hawaiian.

For 30 years, astronomers have been trying to identify why the motions of the Milky Way, our nearest large galaxy neighbor Andromeda, and their smaller neighbors deviate from the overall expansion of the Universe by over 600 km/s (1.3 million mph). The new study shows that roughly half of this motion is generated "locally" from the combination of a pull from the massive nearby Virgo Cluster and our participation in the expansion of the Local Void as it becomes ever emptier.

Representations of the void can be seen in a video (below) and, alternatively, with an interactive model (below). With the interactive model, a viewer can pan, zoom, rotate, and pause/activate the time evolution of movement along orbits. The orbits are shown in a reference frame that removes the overall expansion of the universe. What we are seeing are the deviations from cosmic expansion caused by the interactions of local sources of gravity.


Closest star orbiting our galaxy’s black hole discovered

Astronomers at UCLA university have made a remarkable discovery, after they’ve confirmed the presence of a star orbiting the black hole at the center of our galaxy in a mere 11-and-a-half years – that’s the shortest known orbit of any star near this black hole. The researchers involved in the paper describing the find claim that data will help test Einstein’s theory of relativity, which predicts space and time are warped around the gravitational field of a black hole.

A high-resolution infrared image of the region surrounding the black hole at the center of our galaxy that shows the two orbits of the closest stars. Other orbits are shown in fainter orbits. (c) UCLA

The center of our galaxy is such a hectic place that direct and accurate optical observations around the black hole are simply impossible. Instead, scientists rely on the data they can gather by reading radio, X-ray and infrared waves. To their aid comes the Keck telescope on Mauna Kea in Hawaii, which has been watching stars near the galactic center in IR for 17 years, providing a detailed view of their dynamics. Using the telescope, astronomers answered some of the most puzzling astronomical questions in recent history, thus we now know:

  • at the center of our galaxy, lies a supermassive black hole some 26,000 light years ago, with a mass 4 million times that of our sun.
  • stars accelerate around the supermassive black hole. Further research should confirm the trend for the newly found, fastest orbiting star as well.
  • in 2005, the telescope took the first clear picture of the center of the Milky Way, including the area surrounding the black hole, using laser guide star adaptive optics technology.

The newly confirmed star, dubbed SO-102, has had its orbit completely mapped, thanks to its short period. This is only the second star to have its orbit completely mapped, after the neighboring S0-2. Data from the two orbits together will help astronomers model the black hole itself, as direct IF observations are restricted due to it being invisible. Much of the merit for achieving these immense milestones in astronomy go to Andrea Ghez, leader of the discovery team and a UCLA professor of physics and astronomy who holds the Lauren B. Leichtman and Arthur E. Levine Chair in Astrophysics. Ghez has 3,000 stars that orbit the black hole, and has been studying S0-2 since 1995.

“I’m extremely pleased to find two stars that orbit our galaxy’s supermassive black hole in much less than a human lifetime,” said Ghez.

“It is the tango of S0-102 and S0-2 that will reveal the true geometry of space and time near a black hole for the first time,” Ghez said. “This measurement cannot be done with one star alone.”

The first star with a sufficiently short orbital period to enable a complete three-dimensional reconstruction of its trajectory, SO-2, has an orbital period of around 16 years, but why did SO-102 take so long for it to be discovered? Well, the main reasons is that it’s very faint – around 16 times less brighter than SO-2. Thus, astronomers used the black hole data from prior observations to determine S0-102’s orbital properties, a feat made possible thanks to the Keck telescope’s novel adaptive optics technology, which allows for the 10-meter-diameter mirror to dynamically adjust in order to correct the distorting effects of the Earth’s atmosphere in real time.

“The Keck Observatory has been the leader in adaptive optics for more than a decade and has enabled us to achieve tremendous progress in correcting the distorting effects of the Earth’s atmosphere with high–angular resolution imaging,” Ghez said. “It’s really exciting to have access to the world’s largest and best telescope. It is why I came to UCLA and why I stay at UCLA.”

Milky Way’s dark core that warps time and space

Over time, Ghez and colleagues’ goals have evolved from demonstrating the existence of a black hole at the center of our galaxy, to validating fundamental laws of physics. At high velocities and gravity, Newtonian physics aren’t enough to explain irregularities in elliptical orbits, such as that of Mercury that has an irregular motion due to the sun’s mass to which it is in very close proximity. Measuring the warping effects of the Milky Way’s black hole on spacetime is a lot easier and evident than observations around the sun or similar stars, since the black hole is 4 million times more massive. Long term observations are required, however, in order to spot general relativistic effects, which are cumulative over multiple orbits.


'Exotic Galaxy' With Black Hole Heart Wows Astronomers

A strange, newfound galaxy may help astronomers figure out how black holes and star formation evolved in the early universe, according to a new study.

The spiral galaxy, dubbed Speca, boasts fast-moving jets of particles rushing from its center, a phenomenon more commonly observed in elliptical galaxies. In fact, Speca is just the second spiral known to have such jets.

These jets are spawned by a supermassive black hole at the heart of Speca. Researchers hope studying the galaxy will yield insights into black holes, star birth and the interaction between the two.

"This is probably the most exotic galaxy with a black hole ever seen," said the study's principal investigator Ananda Hota, of the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), in Taiwan, in a statement. "It has the potential to teach us new lessons about how galaxies and clusters of galaxies formed and developed into what we see today." [Photo of the spiral galaxy Speca]

A strange radio galaxy

Speca &mdash whose name is short for Spiral-host Episodic radio galaxy tracing Cluster Accretion &mdash is found about 1.7 billion light-years from Earth. In addition to being a spiral, it's what's known as a radio galaxy.

At the heart of a radio galaxy lies a supermassive black hole. Material surrounding it is thrust outward at relativistic speed, forming jets that shine brightly at radio frequencies. [Images: Black Holes of the Universe]

These relativistic jets aren't constant they ebb and flow with time, likely dependent on the material that fuels them. Over time, the material diffuses into lobes, much as water flowing from a hose spreads out as it slows down.

Most radio galaxies discovered to date are elliptical. Elliptical galaxies tend to be old, without a lot of new star formation, while spirals host much more star birth. So it's intriguing, researchers said, to find a jet-spewing spiral studying Speca could help them better understand how spirals morph into ellipticals over time.

"How black holes stop star formation is still not observed," Hota said. "Speca is an opportunity to investigate these details."

Speca's structure

Astronomers used a variety of telescopes to characterize Speca, finding that it boasts three pairs of lobes. Such a high count is rare even among ellipticals, and it provides clues about the evolution of Speca.

According to Hota, the smallest, closest pair is most likely only a few million years old. The middle lobes fall between 10 and 100 million years old.

But it is the outermost pair that yields the biggest surprise. With an age of several hundred millionyears, the cloud of material spewing from the center of the galaxy diffused long ago, becoming less active over the years.

At some point, however, the material collided with energetic particles streaming throughthe galaxy cluster surrounding Speca. These collisions revived the ancient remnants, providing astronomers with a greater understanding of the environment within the cluster.

The research was published in the August issue of the Monthly Notices of the Royal Astronomical Society.

Understanding star formation

Spiral galaxies eventually transform into ellipticals, and Hota thinks the presence of jets may affect this shift.

"What I believe is that this trend of radio galaxies found always in ellipticals and not in spirals is an end-product of multiple galaxy mergers and multiple episodes of jet feedbacks, happening over a few billion years time," Hota said.

The two combined phenomonena would slowly consume the materials needed for star formation, allowing a spiral galaxy to morph into an elliptical. This meshes well with current theories about how ellipticals form the ejection of material simply speeds the process along.

"These jets are supposed to remove a large fraction of gas from a galaxy and stop further star formation," Hota said. "If the galaxy is gas-rich in the central region, and as the jet direction changes with time, it can have an adverse effect on the star formation history of a galaxy."

Speca provides astronomers with an opportunity to study the effect of the jets on a young galaxy. Since they stem from the supermassive black hole at the galaxy's center, it reveals a connection between the powerful behemoth and the birth of new stars.

"Once we understand how star formation and black hole activity evolved with time, we will have clues on the co-evolution processes," Hota said.


Scientists Discover The Loneliest, Most Isolated Galaxy In The Entire Universe

The galaxy shown at the center of the image here, MCG+01-02-015, is a barred spiral galaxy located . [+] inside a great cosmic void. It is so isolated that if humanity were located in this galaxy instead of our own and developed astronomy at the same rate, we wouldn't have detected the first galaxy beyond our own until the 1960s.

ESA/Hubble & NASA and N. Gorin (STScI) Acknowledgement: Judy Schmidt

Our corner of the Universe was gifted with a plethora of bright, nearby galaxies to light our way through the cosmos.

The Large (top right) and Small (lower left) Magellanic Clouds are visible in the southern skies, . [+] and helped guide Magellan on his famous voyage some 500 years ago. In reality, the LMC is located some 160-165,000 light-years away, with the SMC slightly farther away at 198,000 light-years distant. Along with Triangulum and Andromeda, these four galaxies beyond our own are visible to the naked human eye.

The spirals and ellipticals in our backyard showed us, a century ago, that the Milky Way wasn't alone.

This sketch from the mid-1840s is the first ever one to reveal the spiral structure of any nebula in . [+] the night sky. Now known to be a spiral galaxy, Messier 51, the Whirlpool Galaxy, is one of the most well-studied galaxies beyond our Milky Way.

WILLIAM PARSONS, 3RD EARL OF ROSSE (LORD ROSSE)

Even earlier astronomers still had copious bright galaxies they could observe with their telescopes.

A selection of approximately 2% of the galaxies in the Virgo cluster. There are approximately 1,000 . [+] large galaxies in the Virgo cluster, a large fraction of which were discovered way back in the 18th century. The Virgo cluster is located some 50-60 million light-years away from our Milky Way, and is the largest concentration of galaxies in the extremely nearby Universe.

By measuring the speeds and distances of these galaxies, we discovered the expanding Universe.

The 'raisin bread' model of the expanding Universe, where relative distances increase as the space . [+] (dough) expands. The farther away any two raisin are from one another, the greater the observed redshift will be by time the light is received. The redshift-distance relation predicted by the expanding Universe is borne out in observations, and has been consistent with what's been known all the way back since the 1920s.

Without them, we might never have understood our cosmic origins: the hot Big Bang.

A visual history of the expanding Universe includes the hot, dense state known as the Big Bang and . [+] the growth and formation of structure subsequently. The full suite of data, including the observations of the light elements and the cosmic microwave background, leaves only the Big Bang as a valid explanation for all we see. As the Universe expands, it also cools, enabling ions, neutral atoms, and eventually molecules, gas clouds, stars, and finally galaxies to form.

Unfortunately, not every observer in the Universe gets so lucky.

Streams of dark matter drive the clustering of galaxies and the formation of large-scale structure, . [+] as shown in this KIPAC/Stanford simulation. While the locations where stars, galaxies, and clusters of galaxies emerge are most notable, the enormous cosmic voids separating the matter-rich structures are just as important to understanding our Universe.

O. Hahn and T. Abel (simulation) Ralf Kaehler (visualization)

Most galaxies clump together in groups, clusters, or along filaments, but some reside in underdense regions.

This figure shows the relative attractive and repulsive effects of overdense and underdense regions . [+] on the Milky Way. Note that, despite the large number of galaxies clumped and clustered nearby, there are also large regions that have extremely few galaxies: cosmic voids. While we have a few substantial ones nearby, there are even larger and lower-density voids found in the distant Universe.

Yehuda Hoffman, Daniel Pomarède, R. Brent Tully, and Hélène Courtois, Nature Astronomy 1, 0036 (2017)

The Universe's large-scale structure contains great cosmic voids as well as overdense clumps.

A region of space devoid of matter in our galaxy reveals the Universe beyond, where every point is a . [+] distant galaxy. The cluster/void structure can be seen very clearly. If we were to live in an extremely underdense/void region, we might not have discovered a single galaxy beyond our own until our astronomical tools advanced to near-modern standards.

In these extremely underdense regions, however, galaxies still occasionally form.

Although it's relatively nearby at just 293 million light-years away, the galaxy MCG+01-02-015 has . [+] no other galaxies surrounding it for approximately 100 million light-years in all directions. To the best of our knowledge, it's the loneliest galaxy in the Universe.

ESA/Hubble & NASA and N. Gorin (STScI) Acknowledgement: Judy Schmidt

Although a long-exposure, deep image of MCG+01-02-015 appears to show many other galaxies in its . [+] vicinity, most are far more distant (and a few are closer), but none are within 100 million light-years of the major galaxy itself.

ESA/Hubble & NASA and N. Gorin (STScI) Acknowledgement: Judy Schmidt

In all directions, we find no other galaxies within 100 million light-years of it.

In between the great clusters and filaments of the Universe are great cosmic voids, some of which . [+] can span hundreds of millions of light-years in diameter. While some voids are larger in extent than others, the void that houses MCG+01-02-015 is special because it is so low in density that, rather than having only a few galaxies, it only contains this one known galaxy at all. It is possible, however, that small, low surface brightness galaxies exist in this region after all.

Andrew Z. Colvin (cropped by Zeryphex) / Wikimedia Commons

If we had grown up there, our telescopes would not have observed other galaxies until the 1960s.

Italian astronomer Paolo Maffei's promising work on infrared astronomy culminated in the discovery . [+] of galaxies — like Maffei 1 and 2, shown here — in the plane of the Milky Way itself. Maffei 1, the giant elliptical galaxy at the lower left, is the closest giant elliptical to the Milky Way, yet went undiscovered until 1967. Technology would have needed to advance to approximately these levels to detect a single galaxy beyond MCG+01-02-15.

WISE mission NASA/JPL-Caltech/UCLA

Perhaps we are truly fortunate: our serendipitous position in the Universe allowed us to understand it.

The various galaxies of the Virgo Supercluster, grouped and clustered together. On the largest . [+] scales, the Universe is uniform, but as you look to galaxy or cluster scales, overdense and underdense regions dominate. The full extent of this illustration, which maps out the nearby galaxies to the Milky Way (with us at the center), would have exactly one galaxy in it, MCG+01-02-015, if it were centered on the loneliest galaxy known in the Universe today.


NGC 247, an intermediate spiral galaxy in Cetus

NGC 247 (nicknamed the Needle’s Eye Galaxy) is an elongated intermediate spiral galaxy (although it’s sometimes classified as a dwarf spiral galaxy) of some 70 thousand light-years across, located about 11.1 million light-years away in the constellation of Cetus (the Whale), while it is receding from us at approximately 156 kilometers per second.

It is one of the closest spiral galaxies of the southern sky and is a member of the Sculptor Group, a group of 13 known galaxies that includes the Sculptor Galaxy (NGC 253). Together with several other galaxies, NGC 247 is gravitationally bound to the Sculptor Galaxy. These galaxies form a small core in the center of the Sculptor Group, which is one of the nearest groups of galaxies to the Milky Way.

The distance of NGC 247 was confirmed in late February 2011. Previously it was thought that the galaxy was more than 1 million light-years further away, but that was proved to be wrong.

This nearly edge-on galaxy has a dusty disk and loose and ragged spiral arms, which show large numbers of stars and glowing pink clouds of hydrogen, marking regions of active star formation. NGC 247 has a prominent (foreground) star on its southern edge and a “void” on its northern side (seen to the right of this image) which is a region that contains a paucity of stars and new star formation. This void resembles the eye of a needle, giving the galaxy its nickname.

Apart from the main galaxy itself, this image also reveals numerous galaxies shining far beyond NGC 247. In the upper right of the picture three prominent spirals form a line and still further out, far behind them, many more galaxies can be seen, some shining right through the disk of NGC 247.

This colour image of NGC 247 and its rich backdrop was created from a large number of monochrome exposures taken through blue, yellow/green and red filters taken over many years by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. In addition exposures through a filter that isolates the glow from hydrogen gas have also been included and coloured red. The total exposure times per filter were 20 hours, 19 hours, 25 minutes and 35 minutes, respectively.