Tag Archives: Milky Way

Most Convincing Evidence Yet For Dark Matter Detection

Most Convincing Evidence Yet For Dark Matter Detection

Scientists have been analyzing high-energy gamma rays originating from the center of the Milky Way and have presented the most convincing case so far that at least some of this may come from dark matter.

Dark matter is a type of matter that is thought to account for apparent effects due to mass where no mass can be observed. It behaves differently to normal matter, such as planets and stars, which only accounts for approximately 5% of the universe. It neither emits nor absorbs light or other forms of electromagnetic energy, so a simple definition is that it is matter that does not react to light. The total mass-energy of the known universe is estimated to contain approximately 27% dark matter.

Using data collected from NASA’s Fermi Gamma-ray Space Telescope, scientists from different institutions generated maps of the center of the galaxy. They found that some of the high-energy gamma rays could not be sufficiently explained by known sources. There are numerous known sources of gamma-rays in the center of the galaxy, such as supernova remnants, but it is also predicted to be rich in dark matter. Although scientists know dark matter exists, they are not entirely sure of what it is composed of. Weakly Interacting Massive Particles, or WIMPs, are a strong candidate. It is thought that collision of WIMPs may produce a quickly decaying particle, which could produce gamma rays detectable by Fermi.

Once they removed all the known sources of gamma rays from the Fermi observations, some emission was leftover. If dark matter particles with a particular mass are destroying each other, this would be a remarkable fit for the remaining emission. Despite this, the scientists err on the side of caution since alternative sources may still exist. Further sightings are also required to make this interpretation more convincing.

The Fermi scientists have also turned elsewhere in an attempt to detect dark matter by looking at dwarf galaxies orbiting the Milky Way. Dwarf galaxies are rich in dark matter and lack other types of gamma-ray sources present in the center of the Milky Way which make detection of dark matter problematic. On the flip side, their distance from us and the fact that the dark matter present is still considerably less than that in the center of the Milky Way means that the signals are weak. But according to Elliott Bloom, a member of the Fermi collaboration, “If we ultimately see a significant signal, it could be a very strong confirmation of the dark matter signal claimed in the galactic center.”

While at this stage the signal cannot be confirmed or refuted as dark matter, it represents an exciting step towards the detection of dark matter at the galactic center. 

Check out this YouTube video for an image of the Milky Way with the gamma-ray map from NASA’s Fermi superimposed on top. 

Credit: NASA Goddard; A. Mellinger, CMU; T. Linden, University of Chicago

Read more: http://www.iflscience.com/space/most-convincing-evidence-yet-dark-matter-detection

Youngest Supernova In Milky Way Created By Catastrophic Collision Of Two White Dwarfs

Youngest Supernova In Milky Way Created By Catastrophic Collision Of Two White Dwarfs

Supernovae are some of the brightest objects in the night sky. They are the self-destruction of the largest stars, and on occasion can outshine entire galaxies. One particular type of supernova, involving the catastrophic dance of two stars, has mystified astronomers since it was first discovered in 1941; to date, its not clear what causes a supernova in a binary star system.

After observing the nuclear ashes of the youngest supernova in the Milky Way, a team of astronomers led by Harvard University has come up with a potential answer. At just 110 years old, they have concluded that this violent flash of light was produced by the spectacular collision of two white dwarfs. Publishing their results in the Astrophysical Journal, this finding implies that there are at least three broad ways to destroy a star via a supernova.

In single star systems with at least eight solar masses, the star explodes when it runs out of nuclear fuel to burn. The stars immense gravitational field overcomes the increasingly weak heat emerging from its core, causing it to collapse before undergoing a titanic explosion. Type 1a supernovae, like the one observed in this study, require at least two stars to occur that much, astronomers agree on.

One of the prevailing theories of how they happen is that a white dwarf, a stellar remnant that is unable to undergo fusion in order to produce heat, steals the atmosphere from a companion star. At a critical point, the white dwarf becomes massive enough to exert gargantuan pressures on its core; this initiates a runaway fusion reaction, which immediately leads to its obliteration.

This animation shows two white dwarfs merging. astropage.eu via YouTube

Most astronomers have thought that this companion star was an ageing red giant. However, a recent study revealed that a type 1a supernova was observed burning its nearby companion star, which turned out to be a main sequence star. Either way, the supernova was caused by the theft of another stars atmosphere.

This new study, after observing supernova G1.9+0.3, gives credence to another theory of how type 1a supernovae occur. Using NASAs Chandra X-ray Observatory and the National Science Foundations Jansky Very Large Array, they analyzed the high-energy bursts jettisoning from this young cataclysm. When an object is heated up, it gives off electromagnetic energy, and certain wavelengths apply to certain types of ignition.

The team concludes that the energy regime theyve observed from this particular supernova could only have come about through one event: the collision of two white dwarfs. We observed that the X-ray and radio brightness increased with time, so the data point strongly to a collision between twowhite dwarfsas being the trigger for thesupernova explosionin G1.9+0.3, said co-author Francesca Childs, an astrophysicist at Harvard University, in a statement.

This happens when two closely orbiting white dwarfs lose energy through the emission of gravitational waves, causing them to spiral inwards and merge. During this particular merger, they reached a critical mass that initiates a destructive, runaway fusion reaction, creating a supernova. In light of recent research, this new finding means that there are two ways to create a type 1a supernova, and at least three ways to kill a star overall.

Read more: http://www.iflscience.com/space/youngest-supernova-milky-way-created-catastrophic-collision-two-white-dwarfs

An Immense Spiral Arm Could Encircle The Entire Milky Way

An Immense Spiral Arm Could Encircle The Entire Milky Way

Although we’ve known our galaxy is spiral-shaped for almost a century and a half, our idea of what it looks like as a whole often changes thanks to new discoveries made possible by advances in observational techniques.

It was believed for some time that the Milky Way consisted of four arms, packed with clouds of dust, gas and stars, which emanate outwards in an elegant twist from a central region. But back in 2008, Spitzer data suggested that our galaxy actually only has two arms, extending from a large central bar. Now, it seems that our portrait of the Milky Way has changed once again with the discovery of a new segment of a spiral arm. And, tantalizingly, it could be an extension of a distant arm discovered a couple of years ago, which would mean that one of the arms may wrap around our entire galaxy.

This mighty arm, Scutum-Centaurus, winds outward in a counter-clockwise direction from one end of the Milky Way’s bar, passes between us and the galactic center, and extends all the way to the other side of the galaxy. In 2011, two astronomers from the Harvard-Smithsonian Center for Astrophysics, Thomas Dame and Patrick Thaddeus, spotted an extension of this arm, which placed it outside of our solar system. But now, new data from the Purple Mountain Observatory, China, could suggest that the incredible arm is even longer than that.

For the study, astronomer Yan Sun and colleagues used radio telescope data to look for interstellar gas clouds that mark spiral arms. Rather than looking for the most common ingredient, hydrogen, which is difficult to detect, they hunted radio waves emitted by the second most abundant molecule in interstellar space—carbon monoxide gas.

The researchers focused on clouds located between 46,000 and 67,000 light-years from the galactic center; for some context, our sun is around 27,000 light-years out. As described in The Astrophysical Journal Letters, the scientists found a total of 72 clouds, including 42 that were previously unknown, which line up along a 30,000-light-year-long spiral arm segment. But that’s not the most interesting part. If it turns out to be an extension of the distant segment discovered back in 2011, Scutum-Centaurus may actually make a full 360o turn around the Milky Way. Considering something like that has never been observed in nearby spiral galaxies, it would be pretty incredible if the proposal holds up.

Illustration of the Milky Way, showing the possible extension of Scutum-Centaurus. Credit: Yan Sun/The Astrophysical Journal Letters/NASA/JPL-Caltech/SSC

“It’s rare,” said Dame. “I bet that you would have to look through dozens of face-on spiral galaxy images to find out where you could convince yourself you could track one arm 360 degrees round.”

While the prospect is certainly exciting, there is still the possibility that this arm is not actually part of Scutum-Centaurus at all, but instead a newly discovered lone segment. There exists a problematic 40,000-light-year-long gap between the start of the new arm and the tail of the 2011 extension. However, it shouldn’t take long for scientists to work out whether the arms do indeed join up, as they can start looking for the existence of molecular clouds within this region. If the segments do indeed connect, then we reside in one truly magnificent and unusual galaxy.

[Via Universe Today, Smithsonian, io9 and The Astrophysical Journal Letters]

Read more: http://www.iflscience.com/space/immense-spiral-arm-could-encircle-entire-milky-way

Our Nearest Galactic Neighbor Revealed In Stunning Clarity

Our Nearest Galactic Neighbor Revealed In Stunning Clarity

This stunning new image from the European Southern Observatory (ESO) reveals the closest galaxy to our Milky Way in exquisite detail.

Called IC 1613, it is more accurately a dwarf galaxy,owing to its relatively minute size. Also known as Caldwell 51, this galaxy measures roughly 10,000 light-years across, compared to 100,000 light-years for the Milky Way. It is located about 2.3 million light-years from Earth in the constellation Cetus.

This latest image reveals just how clean the galaxy is, with very little cosmic dust, meaning its innards can be studied in great detail. It was taken by the OmegaCAM camera on the ESOs Very Large Telescope (VLT) Survey Telescope in Chile, and also reveals a cloud of bright pink gas within the galaxy.

Discovered in 1906 by German astronomer Max Wolf, we now know that IC 1613 is part of our Local Group,a neighborhood of more than 50 galaxies. And we know IC 1613s distance from us very precisely, thanks to its cleanliness. This allows us to see distance marker stars, Cepheid variables and RR Lyrae variables, which flash with a regular beat that lets us calculate their distance.

In fact, IC 1613 helped astronomers refine the technique of using these stars to measure distances in the universe, something first proposed by the underappreciated astronomer Henrietta Swan Levitt in the early 20th Century.

Read more: http://www.iflscience.com/space/our-nearest-galactic-neighbour-revealed-stunning-clarity

Fast Dwarf Galaxy Generates Ripples In The Milky Way

Fast Dwarf Galaxy Generates Ripples In The Milky Way

The edge of the Milky Way is not smooth but has ripples, and these ripples have perplexed astronomers since their discovery decades ago. But now we know exactly what caused them.

An international team of astronomers discovered that a small and quick galaxy whizzed past the Milky Way a few hundred years ago. The scientists were able to measure the speed of some of the stars belonging to the dwarf galaxy, which allowed them to work out what actually happened when the fly-by occurred.

Its a bit like throwing a stone into a pond and making ripples, Sukanya Chakrabarti, who presented the findings at the227th meetingof the American Astronomical Society in Florida,said in a statement.Of course we arent talking about a pond, but our galaxy, which is tens of thousands of light-years across, and made of stars and gas, but the result is the same ripples!

Her work is part of a new discipline called galactoseismology, and just like geologists use earthquakes to study the interior of our planet, ripples and interactions allow astronomers to estimate the distribution of matter in a galaxy. This is really the first non-theoretical application of this field, where we can infer things about the unseen composition of galaxies from analyzing galaxic-quakes, said Chakrabarti.

The stars observed are called Cepheid variables, whichare one type of standard candle, objects whose distance can be calculated based on their luminosity.

We have a pretty good idea of the distance to these stars because the intrinsic brightness of Cepheid variable stars depends on their period of pulsation, which we can measure, said Chakrabarti.

What I wanted to know was how fast this speeding bullet was going when it passed by our galaxy with that information we can begin to understand the dynamics, and ultimately how much unseen dark matter is there.

Cepheid VariableRS Puppisas imaged by Hubble(HST).

Dark matter is the dominant type of matter in the universe (making up 84 percent of all matter), but it does not interact with light so we cannot see it. Its effects can be seen on large scales, for example keeping the spiral shape in galaxies or grouping clusters of galaxies in large filaments.

We are yet to directly observe dark matter, but Chakrabarti and her team are looking for more Cepheid variable stars in the halo of the Milky Way to estimate how much dark matter there is in our galaxy.

There could be a population of yet undiscovered Cepheid variables that formed from a gas-rich dwarf galaxy falling into our galaxys halo, said Chakrabarti.With the capabilities of todays telescopes and instruments we should be able to sample enough of the Milky Ways halo to make reasonable estimates on dark matter content one of the greatest mysteries in astronomy today!

Read more: http://www.iflscience.com/space/fast-dwarf-galaxy-generates-ripples-milky-way

Astronomers Have Discovered The Oldest Stars In Our Galaxy

Astronomers Have Discovered The Oldest Stars In Our Galaxy

An international team of astronomers has discovered some of the oldest stars in the Milky Way.In the process, they were able to learna lot about the abundance of different elements in the very early universe.

These stars, which are part of the second generation of stars to form in the universe, were discovered near the very center of the Milky Way and they are believed to have started shining200 million years after the Big Bang. The scientists thinkthat their findings, published in Nature,give an indication ofthe life and death of the very first stars.

The first stars are believed to have been huge, havingup to 1,000 times the mass of the Sun. It is thought that when these objects reached the end of their lives, they exploded inhypernova explosions,tens of times stronger than the supernovae we see in the universe today.The first generation havenot been directly observed yet, but astronomers hope to see them when the James Webb Space Telescope(JWST) starts operation in 2018.

The second generation, including the stars from this study, are metal-poor: They are made almost exclusively of helium and hydrogen, with only traces of heavier elements (the metals). The more metal a star has, the quicker it forms and the smaller it is.

After the Big Bang, the universe was composed of just hydrogen and helium. This is why the first-generation stars were so big.The carbon in our bodies, the oxygen in the air and all the other heavy elements we find in the universe were formed by the first two generations of stars.

The discovery didnt come easy. There are millions of stars in the Milky Ways bulge, so the team had to develop a strategy to make the gargantuan task of observing them in detailmore manageable.

Since very metal-poor stars are slightly bluer than other stars, the researchersselected 14,000 promising stars from the ANU SkyMapper telescope in Australia. Only 23 of themwerethen studied inmore detail in follow-up observations.

There are so many stars in the centerof our galaxy finding these rare stars is really like looking for a needle in a haystack, said co-authorDrAndrew Casey of Cambridges Institute of Astronomy in a statement. But if we select these stars in the right way, its like burning down the farm and sweeping up the needles with a magnet.

The elements released by the first stars act as a chemical signature that is still present in the stars observed in the study.

This work confirms that there are ancient stars in the centre of our galaxy. The chemical signature imprinted on those stars tells us about an epoch in the universe thats otherwise completely inaccessible, said Casey. The universe was probably very different early on, but to know by how much, weve really just got to find more of these stars: more needles in bigger haystacks.

Read more: http://www.iflscience.com/space/discovery-ancient-stars-sheds-light-primordial-hypernovae

Milky Way galaxy has four arms, not two

Milky Way galaxy has four arms, not two

During the 1950s astronomers used data from radio telescopes and determined that our spiral galaxy has four arms. In 2008, images from NASA’s Spitzer Space Telescope showed that the Milky Way only had two arms. However, the conclusion of a 12-year-long study has shown that there are in fact four arms on our galaxy. The results were published in the Monthly Notices of the Royal Astronomical Society.

During the 12 year study, a team of researchers studied around 1650 massive stars with radio telescopes and reconfirmed that based on the distribution and luminosity, there are four arms on the spiral of our galaxy. This contradicts findings from the Spitzer Space Telescope that showed that there are 110 million stars, and those two were confined to two spiral arms, not four.

So how was Spitzer so wrong? Well, the images weren’t exactly wrong, but they weren’t able to see the entire picture. Spitzer works on infrared, and it is able to capture information about stars much like our sun, which are relatively low mass and are cooler. Because this recent data focused on hot, massive stars, Spitzer was blind to them and was unable to factor them in.

Massive stars are somewhat rare and can live for about 10 million years, which is only a blink of an eye on the cosmic time scale. They are born, live, and die within the same arm. Stars that are more like our sun have more time to spin about in the galaxy and spread out. Gravitational pull is only strong enough to collect stars in two of the arms, which Spitzer was able to detect. However, the other two arms have enough compressed gas to allow for massive stars to form. The better astronomers understand the structure of our galaxy, the easier it becomes to understand how and why massive stars form.

Because we are not able to directly observe the entire structure of the Milky Way (on account of being inside it and all), we must rely on observations from instruments like radio telescopes and the Spitzer Space Telescope. Unfortunately, there are times like these when two data sets conflict. This is why it is important for astronomers to factor in all of the evidence before making claims about absolutes, and also to keep revisiting ideas when new evidence is introduced.

Read more: http://www.iflscience.com/space/milky-way-galaxy-has-four-arms-not-two

Largest Age Map Of The Milky Way Confirms It Formed Inside-Out

Largest Age Map Of The Milky Way Confirms It Formed Inside-Out

Understanding how galaxies formis still an open question in astronomy. Researchers think that galaxies grow in a bottom-up paradigm, with smaller objects forming first and then getting progressively bigger. And astronomers have now discovered the most conclusive evidence yetthat this is the case.

An international team of astronomers from the Max Planck Institute and University of Virginahas charted the growth of our own galaxy, the Milky Way. They calculated the ages of 70,000 red giant stars halfway acrossour galaxy up to 50,000 light-years away. They found that the oldest stars were at the center, with younger and younger stars as one moves outwards.

Close to the center of our galaxy, we see old stars that were formed when it was young and small,saidMelissa Ness, lead author of the study,in astatement.Further out, we see young stars. We conclude that our galaxy grew up by growing out.

Calculating the age of stars is not easy. The stars used in this study are red giants,older stars towards theend of their life cycle. Their age can be calculated using their mass, so the team had a huge task in calculating the mass for such a large number of stars.

They looked at stellar oscillations of the red giants using the planet-hunter spacecraftCOROT and Kepler, which allowed them to estimate a mass and thus calculate an age. They comparedthe age estimation from the space telescopes with a different method, spectroscopy,thatestimated the age by looking at the abundance of heavy elements such as nitrogen, carbon, and oxygen. Young stars have a smaller fraction of those elements compared to older ones.

The spectroscopy was obtained using the Apache Point Observatory Galaxy Evolution Experiment (APOGEE). APOGEE is the ideal survey for this work because it can get high-quality spectra for 300 stars simultaneously over a large area of sky, said Steve Majewski, Principal Investigator of the APOGEE survey and coauthor.

Seeing so many stars at once means getting spectra of 70,000 red giants is actually possible with a single telescope in a few years time.

Although evidence of bottom-up growth had already been found, this latest piece of research is the most detailed analysis produced on galaxy formation.

Because we can see so many individual stars in the Milky Way, we can chart its growth in unprecedented detail. This unprecedented, enormous map really is one for the ages, concluded Ness.

Read more: http://www.iflscience.com/space/age-map-milky-way

Ghosts Of Milky Ways Past Revealed By Star Cluster

Ghosts Of Milky Ways Past Revealed By Star Cluster

A surprising fact about galactic astronomy is that we know more about other galaxies thanour own. The Solar System is not in a great place to learn all there is to know about the Milky Way. The origin of our galaxy is still very mysterious, but we might have found a way to learn more about it.

A team of Spanish and Italian astronomers were the first to study the globular clustercalled E 3in detail. Globular clusters are spherical groups of stars that tend to have formed together, so they have approximately the same age.The teamdiscovered a very old system that formed at the very dawn of the Milky Way, with achemical composition that is a lot richer than we expected.

The results have been published in a paper titled “Ghosts of Milky Ways past”in the journal Astronomy & Astrophysics.

“This globular cluster, and a few similar onessuch as Palomar 5 or Palomar 14are `ghosts because they appear to be in the last stages of their existence, and we say from the past because they are very old,”said Carlos de la Fuente Marcos,one of the authors, in astatement.”They were formed when our galaxy was virtually new-born, 13,000 million years ago.”

“Unlike typical globular clusters, which contain hundreds of thousands and in some cases millions of stars, the object studied only has a few tens of thousands of them.”

The Sun belongs to the latest generation of stars that are described as metal-rich, because a small percentage of their mass is made up of elements heavier than hydrogen and helium. Older stars tend to be metal-poor, but the chemical composition of this globular cluster shows the stars having 20 percent of the metallicity of the Sun. This discovery suggests that the metal enrichment started very early in the history of the Milky Way.

This chemical composition is shared among all the stars that are members of the cluster. “This is characteristic of an object that was created in block, in one single episode, like what is supposed to have happened when our galaxy was born: very large star clusters (containing millions of stars) were formed, but what remains of them today are objects like E 3, ghosts from a distant past,” said De la Fuente Marcos.

The team will continue to study the cluster in 2016 in the hopeof answering more questions about the origin of this fascinating object.

Read more: http://www.iflscience.com/cluster-stars-gives-us-clues-about-milky-way-s-past

Our Home Supercluster Gets a Map and a Name

Our Home Supercluster Gets a Map and a Name

Where in the universe is the Milky Way?

Galaxies like ours huddle in clusters, and large-scale systems of galaxies, called superclusters, have vague boundaries that are difficult to define (especially from the inside): They’re all drawn to each other and interconnected in a web of filaments. Now for the first time, astronomers have constructed a map of the local universe. They’ve named our home supercluster Laniakea, Hawaiian for “immeasurable heaven.” The work was published in Nature this week. 

By examining the motions of galaxies, a team of cosmic map makers led by R. Brent Tully from the University of Hawaii charted the distribution of matter in the universe to identify superclusters. A galaxy stuck between two superclusters will be caught in a gravitational tug-of-war. The balance of these forces determines the galaxy’s motion, and measuring the velocity helps define the region of space where each supercluster dominates. With a catalog of 8,000 galaxies’ velocities, the team built a galactic distribution map and located the points where cosmic flows — along which galaxies travel — diverge.

The Laniakea supercluster, they found, is 520 million light-years in diameter and contains the mass of 100 million billion suns within 100,000 galaxies. Its name pays tribute to Polynesian navigators who used knowledge of the heavens to voyage across the Pacific Ocean. 

In the image above, the colors represent density: red for high densities and blue for voids with little matter. Individual galaxies are shown as white dots, and velocity flow streams within the region gravitationally dominated by Laniakea are shown in white. Importantly, the orange line encloses the outer limits of these streams.

The team defined the edge of a supercluster as the boundary at which flow lines diverge: On one side of the line, galaxies flow towards one gravitational center, Nature explains, and beyond it, they flow towards another. “It’s like water dividing at a watershed, where it flows either to the left or right of a height of land,” Tully explains.

After mapping the boundaries of Laniakea, the team discovered that the Milky Way — along with dozens of other galaxies in our Local Group — resides at the outskirts of the supercluster. We’re the blue dot in the picture above. 

“We have finally established the contours that define the supercluster of galaxies we can call home,” Tully says in a news release. “This is not unlike finding out for the first time that your hometown is actually part of much larger country that borders other nations.” 

Laniakea also includes the Virgo cluster (our nearest neighbor, at 55 million light-years away) and Norma-Hydra-Centaurus. The latter is also known as the Great Attractor, which serves as a gravitation focal point that influences the motion of galaxies, Washington Post explains. Our supercluster is flowing towards the Shapley concentration of galaxies, in the upper left corner of the image above.

Image: SDvision interactive visualization software by DP at CEA/Saclay, France

Video: Nature Video

Read more: http://www.iflscience.com/space/our-home-supercluster-gets-map-and-name