Tag Archives: Milky Way

Fastest stars in Milky Way escaped from Large Magellanic Cloud?

Astronomers have proposed that the fastest stars in Milky Way actually escaped from the Large Magellanic Cloud (LMC), the largest nearby satellite dwarf galaxy.

The LMC is the largest and fastest of the dozens of dwarf galaxies in orbit around the Milky Way. It only has 10% of the mass of the Milky Way, and so the fastest runaways born in this dwarf galaxy can easily escape its gravity. The LMC flies around the Milky Way at 400 kilometres per second and, like a bullet fired from a moving train, the speed of these runaway stars is the velocity they were ejected at plus the velocity of the LMC. This is fast enough for them to be the hypervelocity stars. “These stars have just jumped from an express train – no wonder they’re fast,” said co-author Rob Izzard, a Rutherford fellow at the Institute of Astronomy. “This also explains their position in the sky, because the fastest runaways are ejected along the orbit of the LMC towards the constellations of Leo and Sextans.”

Their calculations predict how many hypervelocity stars should be detectable and where in the sky they should be. If right, the data from Gaia, soon to be released, should prove them right or wrong.


Stars in the Milky Way so old they predate it

Astronomers have discovered stars inside the Milky Way that are thought to be so old that they were formed prior to the existence of the galaxy, and that the Milky Way formed around them.

The stars, found near the centre of the Milky Way, are surprisingly pure but contain material from an even earlier star, which died in an enormous explosion called a hypernova. “These pristine stars are among the oldest surviving stars in the Universe, and certainly the oldest stars we have ever seen,” said Louise Howes, lead author of the study published in the latest issue of Nature. “These stars formed before the Milky Way, and the galaxy formed around them,” said Ms Howes, a PhD student at the ANU Research School of Astronomy and Astrophysics.

Not surprisingly, the discovery challenges theories that describe the early universe.


The largest astronomical image ever

Astronomers have assembled the largest single image of the entire Milky Way ever taken.

It is 46 billion pixels across.

The amazing view of the Milky Way was built out of 268 individual views of the galaxy that includes the sun and the Earth, captured night after night over the course of five years with telescopes in Chile’s Atacama Desert. Astronomers at Ruhr-Universität Bochum used the data to examine stars whose brightness changes over time — and the image portrays more than 50,000 new objects with variable brightness that have never been recorded before.


Milky Way’s central black hole is getting active

The uncertainty of science: Sagittarius A* (pronounced A-Star), the Milky Way’s supermassive central black hole, has shown signs of increased activity in recent months.

The new study reveals that Sagittarius A* (Sgr A* for short) has been producing one bright X-ray flare about every ten days. However, within the past year, there has been a ten-fold increase in the rate of bright flares from Sgr A*, at about one every day. This increase happened soon after the close approach to Sgr A* by a mysterious object called G2.

“For several years, we’ve been tracking the X-ray emission from Sgr A*. This includes also the close passage of this dusty object” said Gabriele Ponti of the Max Planck Institute for Extraterrestrial Physics in Germany. “A year or so ago, we thought it had absolutely no effect on Sgr A*, but our new data raise the possibility that that might not be the case.”

G2 was first thought to be a cloud that would be ripped apart as it passed close to Sgr A*, causing an outburst of activity. When it wasn’t ripped apart and there was no immediate increase in activity astronomers concluded that G2 was a star surrounded by dust which was generally unaffected by its close fly-by of the black hole.

The timing of this new activity now is puzzling. It comes much later than it should have if it was caused by G2, but astronomers don’t have any other explanation for it. It might be because of G2’s fly-by, or maybe the activity is just the natural variability of this poorly understand object. Either way it illustrates how little we really know about the behavior of giant black holes.


Mysterious X-rays at the center of the galaxy

The uncertainty of science: The x-ray space telescope NuSTAR has detected high energy x-rays at the center of the Milky Way coming from no obvious source.

In and of themselves, X-rays from the galactic center aren’t unusual. But the X-rays NuSTAR detects don’t seem to be associated with structures already known to exist. For example, a supernova remnant named Sgr A East emits low-energy X-rays but not high-energy X-rays. The high-energy blotch doesn’t correlate with structures seen in radio images either, such as the dust and gas clouds of Sgr A West that are falling toward the supermassive black hole.

Instead, Perez and her colleagues propose that thousands of stellar corpses could be responsible for the high-energy X-rays: massive (and still-growing) white dwarfs, spun-up pulsars, or black holes or neutrons stars feeding on low-mass companion stars.

All of their proposed solutions, however, have serious problems explaining all of the data.


The Milky Way is like ripples in a pond

Milky Way ripples

The uncertainty of science: New survey data of the stars in the Milky Way suggest that the galaxy is not only corrugated with concentric ripples — like you’d see if you dropped a stone in a pond — it is also about 50% larger than previous estimates.

I have watched the size of the Milky Way fluctuate up and down depending on the research for the past forty years. Sometimes it is larger than expected. Sometimes smaller. Without doubt we are getting a better idea of its actual size, but don’t be surprised if the numbers continue to bounce about for decades, even centuries, to come.

The confirmation that the spiral arms are the equivalent of ripples in a pond is also not surprising, as it confirms the intuitive conclusion of anyone who looks at a whirlpool-shaped spiral galaxy: It is a whirlpool spiraling into the gravity well at its center.


New Hubble images to celebrate its upcoming 25th anniversary

The Space Telescope Science Institute (STScI) that operates the Hubble Space Telescope yesterday released two spectacular new images at the January meeting of the American Astronomical Society.

They also announced new data from Hubble that suggests a major eruption had occurred at the center of the Milky Way about two million years ago.


G2 survives Milky Way center fly by

The uncertainty of science: The gas cloud, dubbed G2, that was going to be eaten by the supermassive black hole at the center of the Milky Way as it did a close fly-by this summer has instead turned out to be a massive star formed when the star’s of its binary system merged.

G2 survived the fly-by, produced no big fireworks which were what was predicted if it has been a gas cloud. The data now suggests that the object is instead a very big star formed when two stars merged.

Massive stars in our galaxy, [astronomer Andrea Ghez] noted, primarily come in pairs. When the two stars merge into one, the star expands for more than one million years “before it settles back down,” Ghez said. “This may be happening more than we thought; the stars at the center of the galaxy are massive and mostly binaries. It’s possible that many of the stars we’ve been watching and not understanding may be the end product of a merger that are calm now.”

Be warned that this new hypothesis about G2 has its own uncertainties. Better data might eventually find it to be something else again.


G2 survives fly-by of Milky Way’s supermassive black hole

The uncertainty of science: The mysterious object G2, thought by astronomers to be either a cloud or a star, has survived its close fly-by of Sagittarius A* (pronounced A-star), the supermassive black hole at the center of the Milky Way, without telling scientists whether it is a cloud or a star.

Not only do astronomers still not know clearly what G2 is, the Milky Way’s supermassive black hole continues to behave in ways that baffle them.


New measurements cut dark matter in Milky Way by half

The uncertainty of science: New more robust measurements by Australian astronomers has shown that the amount of dark matter in the Milky Way galaxy is about half of what previous measurements had estimated.

Without doubt something is causing the outer stars in galaxies to orbit their galaxies at much greater speeds than they should. The answer that astronomers have posited since the late 1950s is that there is additional unidentified mass, dubbed dark matter, lurking as a halo around each galaxy, pulling on those outer stars and making them move faster.

The problem remains that no one has as yet detected this unidentified dark matter. Moreover, there are enormous uncertainties in the measurements of the motions of stars. This result helps narrow those uncertainties.


Universal Big Bang lithium deficit confirmed

The uncertainty of science: New data from a globular cluster in nearby dwarf galaxy has confirmed that the deficit of lithium that astronomers have found in the Milky Way also exists in other galaxies.

According to the Big Bang theory, the amount of lithium in the universe should be two or three times more than it is. This result shows that the deficit exists outside the Milky Way, which suggests strongly that something significant is wrong with the Big Bang theory.


The Milky Way’s most distant stars

Astronomers have discovered the two most distant stars of the Milky Way.

Both stars are red giants, aging suns that shine so brightly observers can see them from afar. One star is about 890,000 light-years from Earth in the constellation Pisces—33 times farther from the Milky Way’s center than we are and well beyond the edge of the galactic disk. The only other Milky Way member at a comparable distance is a small galaxy named Leo I, which orbits ours at a distance of 850,000 light-years. If the star in Pisces revolves on a circular path as fast as we do, it takes some eight billion years to complete a single orbit around the galaxy. That’s more than half the age of the universe.

The other newfound star is about 780,000 light-years distant in the constellation Gemini and more than a million light-years from the other star. For comparison, the previous record-breaking individual star was only about half a million light-years from Earth.

Both stars are so far outside the galaxy’s disk that it is quite possible that they are not part of the Milky Way at all.


The Milky Way shrinks

The uncertainty of science: New research by astronomers suggests that the Milky Way is about half as massive as previously estimated.

In the sixties I remember astronomers claiming that the Milky Way was twice as big as Andromeda. Then it was considered half as big. Most recently it was considered about the same size. This new research makes it half as big as Andromeda again.

In other words, the data is very uncertain, and the scientists really don’t have a good handle on it. None of these conclusions should be taken very seriously. All we really know at this point is that the Milky Way and Andromeda are approximately comparable.


Problems with the European Gaia space telescope

Shades of Hubble: The first data from Europe’s Gaia space telescope, launched to map a billion Milky Way stars, will be delayed 9 months while engineers grapple with several problems.

Gaia managers started taking test images early this year, but soon noticed three issues. For one, more light than anticipated is bending around the 10-metre sunshield and entering the telescope.

Small amounts of water trapped in the spacecraft before launch are being released now that the telescope is in the vacuum of space, and more ice than calculated is accumulating on the telescope’s mirrors. In addition, the telescope itself is expanding and contracting by a few dozen nanometres more than expected because of thermal variations.

Mission managers say the number of stars detected will remain the same even if these complications remain untreated, but the accuracy in measurements of the fainter stars will suffer.

Unlike Hubble, however, there is no way to send a shuttle and a team of astronauts to Gaia to fix it. And it sounds like these issues will have an impact on the telescope’s abilities to gather its intended data.

This story raises my hackles for another reason. Gaia was a very technically challenging space telescope to build, but it was far easier and less cutting edge than the James Webb Space Telescope. It also cost far less. What will happen when Webb gets launched later this decade? How likely is it to have similar issues? Based on a story I just completed for Sky & Telescope on the difficulties of building ground-based telescopes, I’d say Webb is very likely to have similar problems, with no way to fix them. The American astronomy community could then be faced with the loss of two decades of research because they had put all the eggs into Webb’s basket, and thus had no money to build anything else.


It turns out that the object dubbed G2 that is zipping past the Milky Way’s central black hole is behaving not like a cloud but more like a star.

The uncertainty of science: It turns out that the object dubbed G2 that is zipping past the Milky Way’s central black hole is behaving not like a cloud but more like a star.

The latest observations by the Keck Observatory in Hawaii show that the gas cloud called “G2” was surprisingly still intact, even during its closest approach to the supermassive black hole at the center of our Milky Way galaxy. Astronomers from the UCLA Galactic Center Group reported today that observations obtained on March 19 and 20, 2014 show the object’s density was still “robust” enough to be detected. This means G2 is not just a gas cloud, but likely has a star inside.

When I wrote a piece about this object for Sky & Telescope I found that among astronomers there was great skepticism about it being just a gas cloud that would be ripped apart when it flew past the black hole. The early data was not conclusive, but enough of it suggested G2 was a star, not a cloud. It turns out here that the skeptics were right.


Using images from the Spitzer Space Telescope, astronomers have assembled a 360 degree zoomable portrait of the plane of the Milky Way galaxy.

Using images from the Spitzer Space Telescope, astronomers have assembled a 360 degree zoomable portrait of the plane of the Milky Way galaxy.

The image is in infrared, which is why it can see parts of the galaxy obscured by dust in visible wavelengths, and you can explore it at your leisure, from home.


The Milky Way’s council of galaxies.

The Milky Way’s council of galaxies.

“All bright galaxies within 20 million light years, including us, are organized in a ‘Local Sheet’ 34-million light years across and only 1.5-million light years thick,” says McCall. “The Milky Way and Andromeda are encircled by twelve large galaxies arranged in a ring about 24-million light years across – this ‘Council of Giants’ stands in gravitational judgment of the Local Group by restricting its range of influence.”

McCall says twelve of the fourteen giants in the Local Sheet, including the Milky Way and Andromeda, are “spiral galaxies” which have highly flattened disks in which stars are forming. The remaining two are more puffy “elliptical galaxies”, whose stellar bulks were laid down long ago. Intriguingly, the two ellipticals sit on opposite sides of the Council. Winds expelled in the earliest phases of their development might have shepherded gas towards the Local Group, thereby helping to build the disks of the Milky Way and Andromeda.


Astronomers announced today the discovery of several dozen stars which are traveling so fast they will escape the Milky Way galaxy.

Astronomers announced today the discovery of 18 sunlike stars which are traveling so fast they will escape the Milky Way galaxy.

These sunlike stars are in addition to another 20 blue giant stars that are also traveling at escape velocity.

The origin of all of these new stars is completely mysterious. The theory had been that such stars got their speed boost by being flung past the galaxy’s central supermassive black hole, dubbed Sagittarius A* (pronounced “A-star”). These new stars, however, come from other directions, and in fact appear to have even come from outside the galaxy’s main disk. Thus, astronomers are baffled as to what caused them to be traveling so fast.


Gaia, a astronomical space probe designed to pinpoint the location of a billion stars to map the Milky Way, was successfully launched today.

Gaia, a astronomical space probe designed to pinpoint the location of a billion stars to map the Milky Way, was successfully launched today.

This is an important spacecraft, but don’t expect to hear anything about its work now for a long time, as it will take a few years to accumulate the data involved and then a years beyond that to analyze it. Nonetheless, when Gaia’s work is finished we will have our first reasonably good map of the Milky Way, with the ability to project that map forward and backward in time.


Linking mass extinctions to the Sun’s journey in the Milky Way

The Sun's orbit in the Milky Way

In a paper published today on the Los Alamos astro-ph preprint service, astronomers propose that as many as eleven past extinction events can be linked to the Sun’s passage through the spiral arms of the Milky Way. (You can download the paper here [pdf].)

A correlation was found between the times at which the Sun crosses the spiral arms and six known mass extinction events. Furthermore, we identify five additional historical mass extinction events that might be explained by the motion of the Sun around our Galaxy. These five additional significant drops in marine genera that we find include significant reductions in diversity at 415, 322, 300, 145 and 33 Myr ago. Our simulations indicate that the Sun has spent ~60% of its time passing through our Galaxy’s various spiral arms.

The figure on the right, from their paper, shows the Sun’s orbit in red over the last half billion years. The Sun’s present position is indicated by the yellow spot, and the eleven extinctions are indicated by the circles.

There are obviously a great deal of uncertainties in this conclusion. Most significantly, the shape and history of the Milky Way remains very much in doubt, especially since we reside within it and cannot really get a good look at it. Though in recent years astronomers have assembled a reasonable image of the galaxy’s shape — a barred spiral with two major arms and several minor ones — this picture includes many assumptions that could very easily be wrong.

Nonetheless, the paper’s conclusions are interesting.
» Read more


Astronomers have compiled the first detailed 3D map of the inner regions of the Milky Way.

Astronomers have compiled the first detailed 3D map of the inner regions of the Milky Way. More here.

They find a box/peanut shaped bulge with an elongated bar and a prominent X-structure, which had been hinted at in previous studies. This indicates that the Milky Way was originally a pure disk of stars, which then formed a thin bar, before buckling into the box/peanut shape seen today.


A survey of planetary nebulae near the Milky Way’s central bulge has revealed that they tend to be aligned with each other.

A survey of planetary nebulae near the Milky Way’s central bulge has revealed that they tend to be aligned with each other.

This discovery is unexpected and suggests that the influence of the bulge, probably its magnetic field, is far greater than predicted.


Part of the gas cloud being ripped apart by the supermassive black hole at the center of the Milky Way have already swung past the black hole.

Part of a gas cloud, being ripped apart by the super massive black hole at the center of the Milky Way, has already swung past the black hole.

“The ionised gas at the head of the cloud is now stretched over more than 150 light-hours (about 160 billion kilometres) at the pericentre of the orbit around the black hole, with the closest approach being about 25 light-hours (or a bit more than 25 billion kilometres)”, explains Stefan Gillessen from MPE, who led the observing team. “The pericentre approach however is not a singular event but rather a process that will be stretching over a period of at least one year.”

The black hole, dubbed Sagittarius A* (pronounced A-star), is more than 4 billion times the mass of our Sun, but emits very little energy for its size. (Most super massive black holes emit energy as they swallow the mass around them.) Astronomers are hoping that they will see some action when it eats this cloud sometime next year.


The remarkable remains of a most recent supernova.

The remarkable remains of a most recent supernova.

Astronomers estimate that a star explodes as a supernova in our Galaxy, on average, about twice per century. In 2008, a team of scientists announced they discovered the remains of a supernova that is the most recent, in Earth’s time frame, known to have occurred in the Milky Way. The explosion would have been visible from Earth a little more than a hundred years ago if it had not been heavily obscured by dust and gas. Its likely location is about 28,000 light years from Earth near the center of the Milky Way.

1 2