galaxies Archives

November 16, 2016November 26, 2016 by Bob King

New Theory of Gravity Does Away With Need for Dark Matter

Erik Verlinde explains his new view of gravity

Let’s be honest. Dark matter’s a pain in the butt. Astronomers have gone to great lengths to explain why is must exist and exist in huge quantities, yet it remains hidden. Unknown. Emitting no visible energy yet apparently strong enough to keep galaxies in clusters from busting free like wild horses, it’s everywhere in vast quantities. What is the stuff – axions, WIMPS, gravitinos, Kaluza Klein particles?

Estimated distribution of matter and energy in the universe. Credit: NASA

It’s estimated that 27% of all the matter in the universe is invisible, while everything from PB&J sandwiches to quasars accounts for just 4.9%. But a new theory of gravity proposed by theoretical physicist Erik Verlinde of the University of Amsterdam found out a way to dispense with the pesky stuff.

formation of complex symmetrical and fractal patterns in snowflakes exemplifies emergence in a physical system. — Snowflakes exemplify the concept of emergence with their complex symmetrical and fractal patterns created when much simpler pieces join together. Credit: Bob King

Unlike the traditional view of gravity as a fundamental force of nature, Verlinde sees it as an emergent property of space. Emergence is a process where nature builds something large using small, simple pieces such that the final creation exhibits properties that the smaller bits don’t. Take a snowflake. The complex symmetry of a snowflake begins when a water droplet freezes onto a tiny dust particle. As the growing flake falls, water vapor freezes onto this original crystal, naturally arranging itself into a hexagonal (six-sided) structure of great beauty. The sensation of temperature is another emergent phenomenon, arising from the motion of molecules and atoms.

So too with gravity, which according to Verlinde, emerges from entropy. We all know about entropy and messy bedrooms, but it’s a bit more subtle than that. Entropy is a measure of disorder in a system or put another way, the number of different microscopic states a system can be in. One of the coolest descriptions of entropy I’ve heard has to do with the heat our bodies radiate. As that energy dissipates in the air, it creates a more disordered state around us while at the same time decreasing our own personal entropy to ensure our survival. If we didn’t get rid of body heat, we would eventually become disorganized (overheat!) and die.

The more massive the object, the more it distorts spacetime. Credit: LIGO/T. Pyle — The more massive the object, the more it distorts space-time, shown here as the green mesh. Earth orbits the Sun by rolling around the dip created by the Sun’s mass in the fabric of space-time. It doesn’t fall into the Sun because it also possesses forward momentum. Credit: LIGO/T. Pyle

Emergent or entropic gravity, as the new theory is called, predicts the exact same deviation in the rotation rates of stars in galaxies currently attributed to dark matter. Gravity emerges in Verlinde’s view from changes in fundamental bits of information stored in the structure of space-time, that four-dimensional continuum revealed by Einstein’s general theory of relativity. In a word, gravity is a consequence of entropy and not a fundamental force.

Space-time, comprised of the three familiar dimensions in addition to time, is flexible. Mass warps the 4-D fabric into hills and valleys that direct the motion of smaller objects nearby. The Sun doesn’t so much “pull” on the Earth as envisaged by Isaac Newton but creates a great pucker in space-time that Earth rolls around in.

In a 2010 article, Verlinde showed how Newton’s law of gravity, which describes everything from how apples fall from trees to little galaxies orbiting big galaxies, derives from these underlying microscopic building blocks.

His latest paper, titled Emergent Gravity and the Dark Universe, delves into dark energy’s contribution to the mix. The entropy associated with dark energy, a still-unknown form of energy responsible for the accelerating expansion of the universe, turns the geometry of spacetime into an elastic medium.

“We find that the elastic response of this ‘dark energy’ medium takes the form of an extra ‘dark’ gravitational force that appears to be due to ‘dark matter’,” writes Verlinde. “So the observed dark matter phenomena is a remnant, a memory effect, of the emergence of spacetime together with the ordinary matter in it.”

Rotation curve of the typical spiral galaxy M 33 (yellow and blue points with errorbars) and the predicted one from distribution of the visible matter (white line). The discrepancy between the two curves is accounted for by adding a dark matter halo surrounding the galaxy. Credit: Public domain / Wikipedia — This diagram shows rotation curves of stars in M33, a typical spiral galaxy. The vertical scale is speed and the horizontal is distance from the galaxy’s nucleus. Normally, we expect stars to slow down the farther they are from galactic center (bottom curve), but in fact they revolve much faster (top curve). The discrepancy between the two curves is accounted for by adding a dark matter halo surrounding the galaxy. Credit: Public domain / Wikipedia

I’ll be the first one to say how complex Verlinde’s concept is, wrapped in arcane entanglement entropy, tensor fields and the holographic principal, but the basic idea, that gravity is not a fundamental force, makes for a fascinating new way to look at an old face.

Physicists have tried for decades to reconcile gravity with quantum physics with little success. And while Verlinde’s theory should be rightly be taken with a grain of salt, he may offer a way to combine the two disciplines into a single narrative that describes how everything from falling apples to black holes are connected in one coherent theory.

November 3, 2016November 11, 2016 by Evan Gough

Somebody Get This Supermassive Black Hole A Towel

Artist's conception of how the "nearly naked" supermassive black hole originated. On the left panel, the black hole begins its encounter with another, larger black hole. In the middle panel, the stars are stripped away. On the right, the black hole emerges from the encounter with only the remnants of its galaxy intact. Credit: Bill Saxton, NRAO/AUI/NSF.

Most galaxies have a super-massive black hole at their centre. As galaxies collide and merge, the black holes merge too, creating the super-massives we see in the universe today. But one team of astronomers went looking for super-massives that aren’t at the heart of galaxies. They looked at over 1200 galaxies, using the National Science Foundation’s (NSF) Very Long Baseline Array (VLBA), and almost all of them had a black hole right where it should be, in the middle of the galaxy itself.

But they did find one hole, in a cluster of galaxies more than two billion light years away from Earth, that was not at the centre of a galaxy. They were surprised too see that this black hole had been stripped naked of surrounding stars. Once they identified this black hole, now called B3 1715+425, they used the Hubble and the Spitzer to follow up. And what they found tells an unusual story.

“We’ve not seen anything like this before.” – James Condon

The super-massive black hole in question, which we’ll call B3 for short, was a curiosity. It was far brighter than anything near it, and it was also more distant than most of the holes they were studying. But a black hole this bright is typically situated at the heart of a large galaxy. B3 had only a remnant of a galaxy surrounding it. It was naked.

James Condon, of the National Radio Astronomy Observatory (NRAO) described what happened.

“We were looking for orbiting pairs of supermassive black holes, with one offset from the center of a galaxy, as telltale evidence of a previous galaxy merger,” said Condon. “Instead, we found this black hole fleeing from the larger galaxy and leaving a trail of debris behind it,” he added.

“We concluded that our fleeing black hole was incapable of attracting that many stars on the way out to make it look like it does now.” – James Condon

Condon and his team concluded that B3 was once a super-massive black hole at the heart of a large galaxy. B3 collided with another, larger galaxy, one with an even larger black hole. During this collision B3 had most of its stars stripped away, except for the ones closest to it. B3 is still speeding away, at more than 2000 km per second.

Nearly Naked Black Hole from NRAO Outreach on Vimeo.

B3 and what’s left of its stars will continue to move through space, escaping their encounter with the other galaxy. It probably won’t escape from the cluster of galaxies it’s in though.

“What happens to a galaxy when most of its stars have been stripped away, but it still has an active super-massive black hole at the middle?” – James Condon

Condon outlines the likely end for B3. It won’t have enough stars and gas surrounding it to trigger new star birth. It also won’t be able to attract new stars. So eventually, the remnant stars of B3’s original galaxy will travel with it, growing progressively dimmer over time.

B3 itself will also grow dimmer, since it has no new material to “feed” on. It will eventually be nearly impossible to see. Only its gravitational effect will betray its position.

“In a billion years or so, it probably will be invisible.” – James Condon

How many B3s are there? If B3 itself will eventually become invisible, how many other super-massive black holes like it are there, undetectable by our instruments? How often does it happen? And how important is it in understanding the evolution of galaxies, and of clusters of galaxies. Condon asks these questions near the end of the clip. For now, at least, we have no answers.

Condon and his team used the NRAO‘s VLBA to search for these lonely holes. The VLBA is a radio astronomy instrument made up of 10 identical 25m antennae around the world, and controlled at a center in New Mexico. The array provides super sharp detail in the radio wave part of the spectrum.

Their black hole search is a long term project, making use of filler time available at the VLBA. Future telescopes, like the Large Synoptic Survey Telescope being built in Chile, will make Condon’s work easier.

Condon worked with Jeremy Darling of the University of Colorado, Yuri Kovalev of the Astro Space Center of the Lebedev Physical Institute in Moscow, and Leonid Petrov of the Astrogeo Center in Falls Church, Virginia. They will report their findings in the Astrophysical Journal.

October 14, 2016November 5, 2016 by Matt Williams

The Universe’s Galaxy Population Just Grew Tenfold

New research indicates that there could be as many as 2 trillion galaxies in the known Universe. Credit: 2MASS/Caltech

Ever since human beings learned that the Milky Way was not unique or alone in the night sky, astronomers and cosmologists have sought to find out just how many galaxies there are in the Universe. And until recently, our greatest scientific minds believed they had a pretty good idea – between 100 and 200 billion.

However, a new study produced by researchers from the UK has revealed something startling about the Universe. Using Hubble’s Deep Field Images and data from other telescopes, they have concluded that these previous estimates were off by a factor of about 10. The Universe, as it turns out, may have had up to 2 trillion galaxies in it during the course of its history.

Led by Prof. Christopher Conselice of the University of Nottingham, U.K., the team combined images taken by the Hubble Space Telescope with other published data to produced a 3-D map of the Universe. They then incorporated a series of new mathematical models that allowed them to infer the existence of galaxies which are not bright enough to be observed by current instruments.

Scientists believe they have found the missing matter of the universe, thus confirming our current cosmological models. Credit: NASA/Chandra — *Scientists from the UK have produced new estimates on the number of galaxies in the Universe, which could shed light on cosmic evolution as well. Credit: NASA/Chandra*

Using these, they then began reviewing how galaxies have evolved over the past 13 billion years. What they learned was quite fascinating. For one, they observed that the distribution of galaxies throughout the history of the Universe was not even. What’s more, they found that in order for everything in their calculations to add up, there had to be 10 times more galaxies in the early Universe than previously thought.

Most of these galaxies would be similar in mass to the satellite galaxies that have been observed around the Milky Way, and would be too faint to be spotted by today’s instruments. In other words, astronomers have only been able to see about 10% of the early Universe until now, because most of its galaxies were too small and faint to be visible.

As Prof. Conselice explained in a Hubble Science Release, while may help resolve a lingering debate about the structure of the 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.”

Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. The goal of the Frontier Fields is to peer back further than the Hubble Ultra Deep Field and get a wealth of images of galaxies as they existed in the first several hundred million years after the Big Bang. Note that the unit of time is not linear in this illustration. Illustration Credit: NASA and A. Feild (STScI) — *Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. Credit: NASA and A. Feild (STScI)*

To break it down, the “top-down model” of galaxy formation states that galaxies formed from huge gas clouds larger than the resulting galaxies. These clouds began collapsing because their internal gravity was stronger than the pressures in the cloud. Based on the speed at which the gas clouds rotated, they would either form a spiral or an elliptical galaxy.

In contrast, the “bottom-up model” states that galaxies formed during the early Universe due to the merging of smaller clumps that were about the size globular clusters. These galaxies could then have been drawn into clusters and superclusters by their mutual gravity.

In addition to helping to resolve this debate, this study also offers a possible solution to the Olbers’ Paradox (aka. “the dark night sky paradox”). Named after the 18th/19th century German astronomer Heinrich Wilhelm Olbers, this paradox addresses the question of why – given the expanse of the Universe and all the luminous matter in it – is the sky dark at night?

Based on their results, the UK team has surmised that while every point in the night sky contains part of a galaxy, most of them are invisible to the human eye and modern telescopes. This is due to a combination of factors, which includes the effects of cosmic redshift, the fact that the Universe is dynamic (i.e. always expanding) and the absorption of light by cosmic dust and gas.

Among other data, scientists used the galaxies visible in the Great Observatories Origins Deep Survey (GOODS) to recalculate the total number of galaxies in the observable Universe. The image was taken by the NASA/ESA Hubble Space Telescope and covers a portion of the southern field of GOODS. This is a large galaxy census, a deep-sky study by several observatories to trace the formation and evolution of galaxies. — *Image was taken by the NASA/ESA Hubble Space Telescope which covers a portion of the southern field of Great Observatories Origins Deep Survey (GOODS). Credit: NASA/ESA/HST*

Needless to say, future missions will be needed to confirm the existence of all these unseen galaxies. And in that respect, Conselice and his colleagues are looking to future missions – ones that are capable of observing stars and galaxies in the non-visible spectrum – to make that happen.

“It boggles the mind that over 90 percent of the galaxies in the universe have yet to be studied,” he added. “Who knows what interesting properties we will find when we discover these galaxies with future generations of telescopes? In the near future, the James Webb Space Telescope will be able to study these ultra-faint galaxies.”

Understanding how many galaxies have existed over time is a fundamental aspect of understanding the Universe as a whole. With every passing study that attempts to resolve what we can see with our current cosmological models, we are getting that much closer!

And be sure to enjoy this video about some of Hubble’s most stunning images, courtesy of HubbleESA:

Further Reading: HubbleSite, Hubble Space Telescope

September 12, 2016September 17, 2016 by Bob King

The Big Dipper in the Year 92,000

Stellar motions distort the future sky. Map: Bob King, Source: Stellarium

If we could transport Ptolemy, a famous astronomer who lived circa 90 – 168 A.D. in Alexandria, Egypt, he would have noticed the shift in position of Arcturus, Sirius and Aldebaran since his time. Everything else would appear virtually unchanged. — If we could transport **Ptolemy**, a famous astronomer who lived circa 90 – 168 A.D. in Alexandria, Egypt, he would have noticed the shift in position of Arcturus, Sirius and Aldebaran since his time. Everything else would appear virtually unchanged.

You go out and look at the stars year after year and never see any of them get up and walk away from their constellations. Take a time machine back to the days of Plato and Socrates and only careful viewing would reveal that just three of the sky’s naked eye stars had budged: Arcturus, Sirius and Aldebaran. And then only a little. Their motion was discovered by Edmund Halley in 1718 when he compared the stars’ positions then to their positions noted by the ancient Greek astronomers. In all three cases, the stars had moved “above a half a degree more Southerly at this time than the Antients reckoned them.”

NGC 4414 is a spiral galaxy that resembles our own Milky Way. I've drawn in the orbits of several stars. Both disk and halo stars orbit about the center but halo stars describe long elliptical orbits. When they plunge through the disk, if they happen to be relatively nearby as is Arcturus, they'll appear to move relatively quickly across the sky. Credit: NASA/ESA — NGC 4414 is a spiral galaxy that resembles our own Milky Way. I’ve drawn in the orbits of several stars. Both disk and halo stars orbit about the center, but halo stars describe long elliptical orbits that take them well beyond the disk. When a star plunges through the disk, if it happens to be relatively nearby as in the case of Arcturus, the star will appear to move relatively quickly across the sky. Both distance and the type of orbit a star has can affect how fast it moves from our perspective. Credit: NASA/ESA with orbits by the author

Stars are incredibly far away. I could throw light years around like I often do here, but the fact is, you can get a real feel for their distance by noting that during your lifetime, none will appear to move individually. The gems of the night and our sun alike revolve around the center of the galaxy. At our solar system’s distance from the center — 26,000 light years or about halfway from center to edge — it takes the sun about 225 million years to make one revolution around the Milky Way.

That’s a LONG time. The other stars we see on a September night take a similar length of time to orbit. Now divide the average lifetime of some 85 years into that number, and you’ll discover that an average star moves something like .00000038% of its orbit around the galactic center every generation. Phew, that ain’t much! No wonder most stars don’t budge in our lifetime.

This graphic, compiled using SkyMap software created by Chris Marriott, shows the motion of Arcturus over — This graphic, made using SkyMap software created by Chris Marriott, shows the motion of Arcturus over a span of 8,000 years.

Sirius, Aldebaran and Arcturus and several other telescopic stars are close enough that their motion across the sky becomes apparent within the span of recorded history. More powerful telescopes, which expand the scale of the sky, can see a great many stars amble within a human lifetime. Sadly, our eyes alone only work at low power!

Precession of Earth's axis maintains it usual 23.5 degree tilt, but this causes the axis to describe a circle in the sky like a wobbling top. Credit: Wikimedia Commons — Precession of Earth’s axis maintains its usual 23.5 degree tilt, but this causes the axis to describe a circle in the sky like a wobbling top. The photo is an animation that repeats 10 seconds, so hang in there. Credit: Wikimedia Commons

But we needn’t invest billions in building a time machine to zing to the future or past to see how the constellation outlines become distorted by the individual motions of the stars that compose them. We already have one! Just fire up a free sky charting software program like Stellarium and advance the clock. Like most such programs, it defaults to the present, but let’s look ahead. Far ahead.

If we advance 90,000 years into the future, many of the constellations would be unrecognizable. Not only that, but more locally, the precession of Earth’s axis causes the polestar to shift. In 2016, Polaris in the Little Dipper stands at the northernmost point in the sky, but in 90,000 years the brilliant star Vega will occupy the spot. Tugs from the sun and moon on Earth’s equatorial bulge cause its axis to gyrate in a circle over a period of about 26,000 years. Wherever the axis points defines the polestar.

I advanced Stellarium far enough into the future to see how radically the Big Dipper changes shape over time. Notice too that Vega will be the polestar in that distant era. Map: Bob King, Source: Stellarium

Take a look at the Big Dipper. Wow! It’s totally bent out of shape yet still recognizable. The Pointer Stars no longer quite point to Polaris, but with some fudging we might make it work. Vega stands near the pole, and being much closer to us than the rest of Lyra’s stars, has moved considerably farther north, stretching the outline of the constellation as if taffy.

Now let's head backwards in time 92,000 years to 90,000 B.C. The Dipper then was fairly unrecognizable, with both Vega and Arcturus near the pole. Map: Bob King , Source: Stellarium — Now let’s head backwards in time 92,000 years to 90,000 B.C. The Dipper then was fairly unrecognizable, with both Vega and Arcturus near the pole. Map: Bob King , Source: Stellarium

Time goes on. We look up at the night sky in the present moment, but so much came before us and much will come after. Constellations were unrecognizable in the past and will be again in the future. In a fascinating discussion with Michael Kauper of the Minnesota Astronomical Society at a recent star party, he described the amount of space in and between galaxies as so enormous that “we’re almost not here” in comparison. I would add that time is so vast we’re likewise almost not present. Make the most of the moment.

September 8, 2016October 5, 2016 by Evan Gough

Best Picture Yet Of Milky Way’s Formation 13.5 Billion Years Ago

The Milky Way is like NGC 4594 (pictured), a disc shaped spiral galaxy with around 200 billion stars. The three main features are the central bulge, the disk, and the halo. Credit: ESO

Maybe we take our beloved Milky Way galaxy for granted. As far as humanity is concerned, it’s always been here. But how did it form? What is its history?

Our Milky Way galaxy has three recognized stellar components. They are the central bulge, the disk , and the halo. How these three were formed and how they evolved are prominent, fundamental questions in astronomy. Now, a team of researchers have used the unique property of a certain type of star to help answer these fundamental questions.

The type of star in question is called the blue horizontal-branch star (BHB star), and it produces different colors depending on its age. It’s the only type of star to do that. The researchers, from the University of Notre Dame, used this property of BHB’s to create a detailed chronographic (time) map of the Milky Way’s formation.

This map has confirmed what theories and models have predicted for some time: the Milky Way galaxy formed through mergers and accretions of small haloes of gas and dust. Furthermore, the oldest stars in our galaxy are at the center, and younger stars and galaxies joined the Milky Way over billions of years, drawn in by the galaxy’s growing gravitational pull.

The team who produced this study includes astrophysicist Daniela Carollo, research assistant professor in the Department of Physics at the University of Notre Dame, and Timothy Beers, Notre Dame Chair of Astrophysics. Research assistant professor Vinicius Placco, and other colleagues rounded out the team.

“We haven’t previously known much about the age of the most ancient component of the Milky Way, which is the Halo System,” Carollo said. “But now we have demonstrated conclusively for the first time that ancient stars are in the center of the galaxy and the younger stars are found at longer distances. This is another piece of information that we can use to understand the assembly process of the galaxy, and how galaxies in general formed.”

This dazzling infrared image from NASA's Spitzer Space Telescope shows hundreds of thousands of stars crowded into the swirling core of our spiral Milky Way galaxy. Credit: NASA/JPL-Caltech — This dazzling infrared image from NASA’s Spitzer Space Telescope shows hundreds of thousands of stars crowded into the swirling core of our spiral Milky Way galaxy. Credit: NASA/JPL-Caltech

The Sloan Digital Sky Survey (SDSS) played a key role in these findings. The team used data from the SDSS to identify over 130,000 BHB’s. Since these stars literally “show their age”, mapping them throughout the Milky Way produced a chronographic map which clearly shows the oldest stars near the center of the galaxy, and youngest stars further away.

“The colors, when the stars are at that stage of their evolution, are directly related to the amount of time that star has been alive, so we can estimate the age,” Beers said. “Once you have a map, then you can determine which stars came in first and the ages of those portions of the galaxy. We can now actually visualize how our galaxy was built up and inspect the stellar debris from some of the other small galaxies being destroyed by their interaction with ours during its assembly.”

Astronomers infer, from various data-driven approaches, that different structural parts of the galaxy have different ages. They’ve assigned ages to different parts of the galaxy, like the bulge. That makes sense, since everything can’t be the same age. Not in a galaxy that’s this old. But this map makes it even clearer.

As the authors say in their paper, “What has been missing, until only recently, is the ability to assign ages to individual stellar populations, so that the full chemo-dynamical history of the Milky Way can be assessed.”

This new map, with over 130,000 stars as data points, is a pretty important step in understanding the evolution of the Milky Way. It takes something that was based more on models and theory, however sound they were, and reinforces it with more constrained data.

Update: The chronographic map, as well as a .gif, can be viewed here.

September 7, 2016September 11, 2016 by Bob King

Terzan 5 May Unlock Secret to Milky Way’s Past

Peering through the thick dust clouds of the galactic bulge (center of the galaxy) an international team of astronomers has revealed the unusual mix of stars in the stellar cluster known as Terzan 5. The new results indicate that Terzan 5 is in fact one of the bulge's primordial building blocks, most likely the relic of the very early days of the Milky Way. Credit: NASA/ESA/Hubble/F. Ferraro

Peering through the thick dust clouds of the galactic bulge an international team of astronomers has revealed the unusual mix of stars in the stellar cluster known as Terzan 5. The new results indicate that Terzan 5 is in fact one of the bulge's primordial building blocks, most likely the relic of the very early days of the Milky Way. Credit: NASA/ESA/Hubble/F. Ferraro — Peering through the thick dust clouds of the galactic bulge (center of the galaxy) an international team of astronomers has revealed the unusual mix of stars in the stellar cluster known as Terzan 5. The new results indicate that Terzan 5 is in fact one of the bulge’s primordial building blocks, most likely the relic of the very early days of the Milky Way. Credit: NASA/ESA/Hubble/F. Ferraro

Not many people have heard of the globular star cluster Terzan 5. It’s a big ball of stars resembling spilled sugar like so many other globular clusters. A very few globulars are bright enough to see with the naked eye; Terzan 5 is faint because it lies far away in the direction of the center of Milky Way galaxy inside its central bulge. Here, the stars that formed at the galaxy’s birth are packed together in great numbers. They are the “old ones” of the Milky Way.

Today, a team of astronomers revealed that Terzan 5 is unlike any globular cluster known. Most Milky Way globulars contain stars of just one age, about 11-12 billion years. They formed around the same time as the Milky Way itself, used up all their available gas early to build stars and then spent the remaining billions of years aging. Most orbit the galaxy’s center in a vast halo like moths whirring around a bright light. Oddball Terzan 5 has two populations aged 12 billion and 4.5 billion years old and it’s located inside the galactic bulge.

Globular clusters are distributed in a spherical halo about the core or bulge in the Milky Way galaxy. The Sun and planets are located well away from the center. From our perspective, most globular clusters appear concentrated in the direction of the galaxy's center. Credit: Science Frontiers Online — Globular clusters are distributed in a spherical halo about the star-rich core or bulge at the center of the disk of the Milky Way galaxy. Credit: Science Frontiers Online

The team used the cameras on the Hubble Space Telescope as well as a host of ground-based telescopes to find compelling evidence for the two distinct kinds of stars. Not only do they show a large gap in age, but the differ in the elements they contain. Terzan 5’s dual populations point to a star formation process that wasn’t continuous but dominated by two distinct bursts of star formation.

“This requires the Terzan 5 ancestor to have large amounts of gas for a second generation of stars and to be quite massive. At least 100 million times the mass of the Sun,” explains Davide Massari, co-author of the study.

Its unusual properties make Terzan 5 the ideal candidate for the title of “living fossil” from the early days of the Milky Way. Current theories on galaxy formation assume that vast clumps of gas and stars interacted to form the primordial bulge of the Milky Way, merging and dissolving in the process.

While the properties of Terzan 5 are uncommon for a globular cluster, they’re very similar to the stars found in the galactic bulge. Remnants of those gaseous clumps appear to have stuck around intact since the days of our galaxy’s birth, one of them evolving into the present day Terzan 5. That makes it a relic from the Milky Way’s infant days and one of the earliest galactic building blocks. Later, the cluster, which held onto some of its remaining gas, experienced a second burst of star formation.

This current model of the Milky Way galaxy shows the yellow-hued galactic bulge formed by ancient stars well along in their evolution, in contrast to the bluer, younger stars in the spiral arms. Credit: NASA/JPL-Caltech/R. Hurt (SSC/Caltech)

“Some characteristics of Terzan 5 resemble those detected in the giant clumps we see in star-forming galaxies at high-redshift (galaxies just beginning to form in the remote universe in the far distant past), suggesting that similar assembling processes occurred in the local and in the distant universe at the epoch of galaxy formation,” said Dr. Francesco Ferraro from the University of Bologna, Italy, who headed up the team.

The Milky Way on a late September night offers an opportunity to contemplate the grand form of the galaxy. Credit: Bob King

Terzan 5’s chandelier-like presence is helping astronomers understand how our galaxy was assembled. Reconstructing the past is one of the key occupations of astronomy. The present is continually departing with every passing moment. Soon enough, every piece of information slips into the past tense. In the near-past, which records humanity’s comings and goings, details are often forgotten or lost. The deep past is even worse. With no one around and only scattered clues, astronomers continually look for fragmental remains that when woven into the fabric of a theory, reveal patterns and processes before we came to be.

June 2, 2016June 13, 2016 by Evan Gough

New ‘Einstein Ring’ Discovered By Dark Energy Camera

The "Canarias Einstein Ring." The green-blue ring is the source galaxy, the red one in the middle is the lens galaxy. The lens galaxy has such strong gravity, that it distorts the light from the source galaxy into a ring. Because the two galaxies are aligned, the source galaxy appears almost circular. Image: This composite image is made up from several images taken with the DECam camera on the Blanco 4m telescope at the Cerro Tololo Observatory in Chile.

A rare object called an Einstein Ring has been discovered by a team in the Stellar Populations group at the Instituto de Astrofísica de Canarias (IAC) in Spain. An Einstein Ring is a specific type of gravitational lensing.

Einstein’s Theory of General Relativity predicted the phenomena of gravitational lensing. Gravitational lensing tells us that instead of travelling in a straight line, light from a source can be bent by a massive object, like a black hole or a galaxy, which itself bends space time.

Einstein’s General Relativity was published in 1915, but a few years before that, in 1912, Einstein predicted the bending of light. Russian physicist Orest Chwolson was the first to mention the ring effect in scientific literature in 1924, which is why the rings are also called Einstein-Chwolson rings.

Gravitational lensing is fairly well-known, and many gravitational lenses have been observed. Einstein rings are rarer, because the observer, source, and lens all have to be aligned. Einstein himself thought that one would never be observed at all. “Of course, there is no hope of observing this phenomenon directly,” Einstein wrote in 1936.

The team behind the recent discovery was led by PhD student Margherita Bettinelli at the University of La Laguna, and Antonio Aparicio and Sebastian Hidalgo of the Stellar Populations group at the Instituto de Astrofísica de Canarias (IAC) in Spain. Because of the rarity of these objects, and the strong scientific interest in them, this one was given a name: The Canarias Einstein Ring.

There are three components to an Einstein Ring. The first is the observer, which in this case means telescopes here on Earth. The second is the lens galaxy, a massive galaxy with enormous gravity. This gravity warps space-time so that not only are objects drawn to it, but light itself is forced to travel along a curved path. The lens lies between Earth and the third component, the source galaxy. The light from the source galaxy is bent into a ring form by the power of the lens galaxy.

When all three components are aligned precisely, which is very rare, the light from the source galaxy is formed into a circle with the lens galaxy right in the centre. The circle won’t be perfect; it will have irregularities that reflect irregularities in the gravitational force of the lens galaxy.

Another Einstein Ring. This one is named LRG 3-757. This one was discovered by the Sloan Digital Sky Survey, but this image was captured by Hubble's Wide Field Camera 3. Image: NASA/Hubble/ESA — Another Einstein Ring. This one is named LRG 3-757. This one was discovered by the Sloan Digital Sky Survey, but this image was captured by Hubble’s Wide Field Camera 3. Image: NASA/Hubble/ESA

The objects are more than just pretty artifacts of nature. They can tell scientists things about the nature of the lens galaxy. Antonio Aparicio, one of the IAC astrophysicists involved in the research said, “Studying these phenomena gives us especially relevant information about the composition of the source galaxy, and also about the structure of the gravitational field and of the dark matter in the lens galaxy.”

Looking at these objects is like looking back in time, too. The source galaxy is 10 billion light years from Earth. Expansion of the Universe means that the light has taken 8.5 billion light years to reach us. That’s why the ring is blue; that long ago, the source galaxy was young, full of hot blue stars.

The lens itself is much closer to us, but still very distant. It’s 6 billion light years away. Star formation in that galaxy likely came to a halt, and its stellar population is now old.

The discovery of the Canarias Einstein Ring was a happy accident. Bettinelli was pouring over data from what’s known as the Dark Energy Camera (DECam) of the 4m Blanco Telescope at the Cerro Tololo Observatory, in Chile. She was studying the stellar population of the Sculptor dwarf galaxy for her PhD when the Einstein Ring caught her attention. Other members of the Stellar Population Group then used OSIRIS spectrograph on the Gran Telescopio CANARIAS (GTC) to observe and analyze it further.

April 18, 2016April 8, 2018 by Evan Gough

Dwarf Dark Matter Galaxy Hides In Einstein Ring

The large blue light is a lensing galaxy in the foreground, called SDP81, and the red arcs are the distorted image of a more distant galaxy. By analyzing small distortions in the red, distant galaxy, astronomers have determined that a dwarf dark galaxy, represented by the white dot in the lower left, is companion to SDP81. The image is a composite from ALMA and the Hubble. Image: Y. Hezaveh, Stanford Univ./ALMA (NRAO/ESO/NAOJ)/NASA/ESA Hubble Space Telescope — The large blue light is a lensing galaxy in the foreground, called SDP81, about 4 billion light years away. The red arcs are the distorted image of a more distant galaxy, about 12 billion light years away. By analyzing small distortions in the red, distant galaxy, astronomers have determined that a dwarf dark galaxy, represented by the white dot in the lower left, is bound to SDP81. The image is a composite from ALMA and the Hubble. Image: Y. Hezaveh, Stanford Univ./ALMA (NRAO/ESO/NAOJ)/NASA/ESA Hubble Space Telescope

Everybody knows that galaxies are enormous collections of stars. A single galaxy can contain hundreds of billions of them. But there is a type of galaxy that has no stars. That’s right: zero stars.

These galaxies are called Dark Galaxies, or Dark Matter Galaxies. And rather than consisting of stars, they consist mostly of Dark Matter. Theory predicts that there should be many of these Dwarf Dark Galaxies in the halo around ‘regular’ galaxies, but finding them has been difficult.

Now, in a new paper to be published in the Astrophysical Journal, Yashar Hezaveh at Stanford University in California, and his team of colleagues, announce the discovery of one such object. The team used enhanced capabilities of the Atacamas Large Millimeter Array to examine an Einstein ring, so named because Einstein’s Theory of General Relativity predicted the phenomenon long before one was observed.

An Einstein Ring is when the massive gravity of a close object distorts the light from a much more distant object. They operate much like the lens in a telescope, or even a pair of eye-glasses. The mass of the glass in the lens directs incoming light in such a way that distant objects are enlarged.

Einstein Rings and gravitational lensing allow astronomers to study extremely distant objects, by looking at them through a lens of gravity. But they also allow astronomers to learn more about the galaxy that is acting as the lens, which is what happened in this case.

If a glass lens had tiny water spots on it, those spots would add a tiny amount of distortion to the image. That’s what happened in this case, except rather than microscopic water drops on a lens, the distortions were caused by tiny Dwarf Galaxies consisting of Dark Matter. “We can find these invisible objects in the same way that you can see rain droplets on a window. You know they are there because they distort the image of the background objects,” explained Hezaveh. The difference is that water distorts light by refraction, whereas matter distorts light by gravity.

As the ALMA facility increased its resolution, astronomers studied different astronomical objects to test its capabilities. One of these objects was SDP81, the gravitational lens in the above image. As they examined the more distant galaxy being lensed by SDP81, they discovered smaller distortions in the ring of the distant galaxy. Hezaveh and his team conclude that these distortions signal the presence of a Dwarf Dark Galaxy.

But why does this all matter? Because there is a problem in the Universe, or at least in our understanding of it; a problem of missing mass.

Our understanding of the formation of the structure of the Universe is pretty solid, at least in the larger scale. Predictions based on this model agree with observations of the Cosmic Microwave Background (CMB) and galaxy clustering. But our understanding breaks down somewhat when it comes to the smaller scale structure of the Universe.

One example of our lack of understanding in this area is what’s known as the Missing Satellite Problem. Theory predicts that there should be a large population of what are called sub-halo objects in the halo of dark matter surrounding galaxies. These objects can range from things as large as the Magellanic Clouds down to much smaller objects. In observations of the Local Group, there is a pronounced deficit of these objects, to the tune of a factor of 10, when compared to theoretical predictions.

Because we haven’t found them, one of two things needs to happen: either we get better at finding them, or we modify our theory. But it seems a little too soon to modify our theories of the structure of the Universe because we haven’t found something that, by its very nature, is hard to find. That’s why this announcement is so important.

The observation and identification of one of these Dwarf Dark Galaxies should open the door to more. Once more are found, we can start to build a model of their population and distribution. So if in the future more of these Dwarf Dark Galaxies are found, it will gradually confirm our over-arching understanding of the formation and structure of the Universe. And it’ll mean we’re on the right track when it comes to understanding Dark Matter’s role in the Universe. If we can’t find them, and the one bound to the halo of SDP81 turns out to be an anomaly, then it’s back to the drawing board, theoretically.

It took a lot of horsepower to detect the Dwarf Dark Galaxy bound to SDP81. Einstein Rings like SDP81 have to have enormous mass in order to exert a gravitational lensing effect, while Dwarf Dark Galaxies are tiny in comparison. It’s a classic ‘needle in a haystack’ problem, and Hezaveh and his team needed massive computing power to analyze the data from ALMA.

ALMA will consist of 66 individual antennae like these when it is complete. The facility is located in the Atacama Desert in Chile, at 5,000 meters above sea level. Credit: ALMA (ESO / NAOJ / NRAO)

ALMA, and the methodology developed by Hezaveh and team will hopefully shed more light on Dwarf Dark Galaxies in the future. The team thinks that ALMA has great potential to discover more of these halo objects, which should in turn improve our understanding of the structure of the Universe. As they say in the conclusion of their paper, “… ALMA observations have the potential to significantly advance our understanding of the abundance of dark matter substructure.”

March 24, 2016April 12, 2016 by Evan Gough

Most ‘Outrageous’ Luminous Galaxies Ever Observed

An artist's conception of an extremely luminous infrared galaxy similar to the ones reported in this paper. Image credit: NASA/JPL-Caltech.

Astronomers might be running out of words when it comes to describing the brightness of objects in the Universe.

Luminous, Super-Luminous, Ultra-Luminous, Hyper-Luminous. Those words have been used to describe the brightest objects we’ve found in the cosmos. But now astronomers at the University of Massachusetts Amherst have found galaxies so bright that new adjectives are needed. Kevin Harrington, student and lead author of the study describing these galaxies, says, “We’ve taken to calling them ‘outrageously luminous’ among ourselves, because there is no scientific term to apply.”

The terms “ultra-luminous” and “hyper-luminous” have specific meanings in astronomy. An infrared galaxy is called “ultra-luminous” when it has a rating of about 1 trillion solar luminosities. At 10 trillion solar luminosities, the term “hyper-luminous” is used. For objects greater than that, at around 100 trillion solar luminosities, “we don’t even have a name,” says Harrington.

The size and brightness of these 8 galaxies is astonishing, and their existence comes as a surprise. Professor Min Yun, who leads the team, says, “The galaxies we found were not predicted by theory to exist; they’re too big and too bright, so no one really looked for them before.” These newly discovered galaxies are thought to be about 10 billion years old, meaning they were formed about 4 billion years after the Big Bang. Their discovery will help astronomers understand the early Universe better.

“Knowing that they really do exist and how much they have grown in the first 4 billion years since the Big Bang helps us estimate how much material was there for them to work with. Their existence teaches us about the process of collecting matter and of galaxy formation. They suggest that this process is more complex than many people thought,” said Yun.

Gravitational lensing plays a role in all this though. The galaxies are not as large as they appear from Earth. As their light passes by massive objects on its way to Earth, their light is magnified. This makes them look 10 times brighter than they really are. But event taking gravitational lensing into account, these are still impressive objects.

But it’s not just the brightness of these objects that are significant. Gravitational lensing of a galaxy by another galaxy is rare. Finding 8 of them is unheard of, and could be “another potentially important discovery,” says Yun. The paper highlights these galaxies as being among the most interesting objects for further study “because the magnifying property of lensing allows us to probe physical details of the intense star formation activities at sub-kpc scale…”

The team’s analysis also shows that the extreme brightness of these galaxies is caused solely by star formation.“The Milky Way produces a few solar masses of stars per year, and these objects look like they forming one star every hour,” Yun says. Harrington adds, “We still don’t know how many tens to hundreds of solar masses of gas can be converted into stars so efficiently in these objects, and studying these objects might help us to find out.”

It took a tag team of telescopes to discover and confirm these outrageously luminous galaxies. The team of astronomers, led by Professor Min Yun, used the 50 meter diameter Large Millimeter Telescope for this work. It sits atop an extinct volcano in Mexico, the 15,000 foot Sierra Negra. They also relied on the Herschel Observatory, and the Planck Surveyor.

March 14, 2016March 18, 2016 by Evan Gough

The Milky Way Galaxy’s Dark Halo Of Star Formation

Dark matter is invisible. Based on the effect of gravitational lensing, a ring of dark matter has been inferred in this image of a galaxy cluster (CL0024+17) and has been represented in blue. Image: NASA/ESA.

Dark Matter is rightly called one of the greatest mysteries in the Universe. In fact, so mysterious is it, that we here in the opulent sky-scraper offices of Universe Today often joke that it should be called “Dark Mystery.” But that sounds like a cheesy History Channel show, and here at Universe Today we don’t like cheesy, so Dark Matter it remains.

Though we still don’t know what exactly Dark Matter is, we keep learning more about how it interacts with the rest of the Universe, and nibbling around at the edges of what it might be. But before we get into the latest news about Dark Matter, it’s worth stepping back a bit to remind ourselves of what is known about Dark Matter.

Evidence from cosmology shows that about 25% of the mass of the Universe is Dark Matter, also known as non-baryonic matter. Baryonic matter is ‘normal’ matter, which we are all familiar with. It’s made up of protons and neutrons, and it’s the matter that we interact with every day.

Cosmologists can’t see the 25% of matter that is Dark Matter, because it doesn’t interact with light. But they can see the effect it has on the large scale structure of the Universe, on the cosmic microwave background, and in the phenomenon of gravitational lensing. So they know it’s there.

Large galaxies like our own Milky Way are surrounded by what is called a halo of Dark Matter. These huge haloes are in turn surrounded by smaller sub-haloes of Dark Matter. These sub-haloes have enough gravitational force to form dwarf galaxies, like the Milky Way’s own Sagittarius and Canis Major dwarf galaxies. Then, these dwarf galaxies themselves have their own Dark Matter haloes, which at this scale are now much too small to contain gas or stars. Called dark satellites, these smaller haloes are of course invisible to telescopes, but theory states they should be there.

But proving that these dark satellites are even there requires some evidence of the effect they have on their host galaxies.

Now, thanks to Laura Sales, who is an assistant professor at the University of California, Riverside’s, Department of Physics and Astronomy, and her collaborators at the Kapteyn Astronomical Institute in the Netherlands, Tjitske Starkenberg and Amina Helmi, there is more evidence that these dark satellites are indeed there.

In their paper “Dark influences II: gas and star formation in minor mergers of dwarf galaxies with dark satellites,” from November 2015, they provide an analysis of theory-based computer simulations of the interaction between a dwarf galaxy and a dark satellite.

Their paper shows that when a dark satellite is at its closest point to a dwarf galaxy, the satellite’s gravitational influence compresses the gas in the dwarf. This causes a sustained period of star formation, called a starburst, that can last for billions of years.

NGC 5253 is one of the nearest of the known Blue Compact Dwarf (BCD) galaxies, and is located at a distance of about 12 million light-years from Earth in the southern constellation of Centaurus. It is experiencing a starburst of hot, young stars, which could be caused by dark satellites. Image: NASA/ESA/Hubble.

Their modelling suggests that dwarf galaxies should be exhibiting a higher rate of star formation than would otherwise be expected. And observation of dwarf galaxies reveals that that is indeed the case. Their modelling also suggests that when a dark satellite and a dwarf galaxy interact, the shape of the dwarf galaxy should change. And again, this is born out by the observation of isolated spheroidal dwarf galaxies, whose origin has so far been a mystery.

The exact nature of Dark Matter is still a mystery, and will probably remain a mystery for quite some time. But studies like this keep shining more light on Dark Matter, and I encourage readers who want more detail to read it.