On Friday night, a rare lunar phenomenon will occur called a black moon — or rather, the second new moon within a one-month period. It’s a remarkable scientific event, but for those of you who want to witness it with you own eyes, you’re going to have some trouble.
NASA has had enough of astrology. Astronomers have spent years patiently trying to explain why zodiac signs are not science, and NASA finally seems fed up with the public’s obsession with them. NASA just dropped the ultimate astrology smackdown in a Tumblr post that’s since gone viral.
“Cannon herself was responsible for classifying, by hand, more stars in a lifetime than anyone else: around 350,000. She could classify a single star, fully, in approximately 20 seconds, and used a magnifying glass for the majority of the (faint) stars. Her legacy is now nearly 100 years old: on May 9, 1922, the International Astronomical Union formally adopted Annie Jump Cannon’s stellar classification system. With only minor changes having been made in the 94 years since, it is still the primary system in use today.”
A look up at the stars in the night sky shows a clear distinction: some are fainter while others are brighter, some are redder while others are bluer, some are closer while others are much farther away. But what accounts for the differences – some real and some only apparent – between these stars? For most of human history, not only didn’t we know, but any distinction or classification scheme seemed arbitrary. In the 1800s, a new tool, stellar spectroscopy, enabled us to break up the light from stars into its individual wavelengths. By observing a number of “dark” features in these spectra, corresponding to atoms, ions and their absorption lines, we could finally start to make sense of it, and a more objective system.
The surprising discovery of a massive, Milky
Way-size galaxy that is made of 99.99 percent dark matter has
astronomers dreaming up new ideas about how galaxies form.
Among the thousand-plus galaxies in the Coma cluster, a massive clump
of matter some 300 million light-years away, is at least one — and
maybe a few hundred — that shouldn’t exist.
Dragonfly 44 is a dim galaxy, with one star for every hundred in our
Milky Way. But it spans roughly as much space as the Milky Way. In
addition, it’s heavy enough to rival our own galaxy in mass, according to results published in the Astrophysical Journal Letters at
the end of August. That odd combination is crucial: Dragonfly 44 is so
dark, so fluffy, and so heavy that some astronomers believe it will
either force a revision of our theories of galaxy formation or help us
understand the properties of dark matter, the mysterious stuff that
interacts with normal matter via gravity and not much else. Or both.
The discovery came almost by accident. The astronomers Pieter van Dokkum of Yale University and Roberto Abraham of
the University of Toronto were interested in testing theories of how
galaxies form by searching for objects that have been invisible to even
the most advanced telescopes: faint, wispy and extended objects in the
sky. So their team built the Dragonfly Telephoto Array,
a collection of modified Canon lenses that focus light onto commercial
camera sensors. This setup cut down on any scattered light inside the
system that might hide a dim object.
The plan was to study the faint fringes of nearby galaxies. But the
famous Coma cluster — the collection of galaxies that long ago inspired
astronomer Fritz Zwicky’s conjecture that such a thing as dark matter
might exist — beckoned. “Partway through, we just could not resist
looking at Coma,” Abraham said. “You could argue that this discovery
emerged from a lack of discipline.” They planned to study the Coma
cluster’s intracluster light — the faint glow of loose stars floating
between the cluster’s galaxies.
Instead, they found 47 faint smudges
that wouldn’t go away. These smudges seemed to have diameters roughly
the same size as the Milky Way. Yet according to the commonly accepted
models of galaxy formation, anything that big shouldn’t be so dim.
In these theories, clumps of dark matter seed the universe with
light. First, clouds of dark matter coalesce into relatively dense
dark-matter haloes. Then gas and fragments of other galaxies, drawn by
the halo’s gravity, collect at the center. They spin out into a disk and
collapse into luminous stars to form something we can see through
telescopes. The whole process seems to be reasonably predictable for big
galaxies such as our Milky Way. Having measured either a galaxy’s
dark-matter halo or its assortment of stars, you should be able to
predict the other to within a factor of two.
The dark galaxy Dragonfly 44. The scale bar represents a distance of 10 kiloparsecs, or about 33,000 light years.
“It’s not just dogma. It’s basically that there are no exceptions that we knew of,” said Jeremiah Ostriker, an astrophysicist at Columbia University.
After Abraham and van Dokkum realized that they appeared to be
looking at 47 exceptions, they did a search through the literature. They
found that similar fuzzy blobs have been on the edge of discovery since
the 1970s. Van Dokkum thinks astronomy’s transition from photographic
plates — which were perhaps better suited to picking up extended,
diffuse objects — to modern digital sensors may actually have hid them
from further attention.
Abraham and van Dokkum first noticed their smudges in the spring of
2014. Since then, similar “ultra-diffuse galaxies,” or UDGs, have been
discovered in other galaxy groupings like the Virgo and Fornax clusters.
And in the Coma cluster, one study suggested, there may be a thousand more of them, including 332 that are about as large as the Milky Way.
Meanwhile, the Dragonfly team has been advancing the case that these
new dim galaxies really are oddballs that challenge current theory.
They’re failed galaxies, this argument holds. Dark matter planted the
seeds of a spiral disk and stars, but somehow the luminous structure
That argument has convinced outside experts like Ostriker, who finds
van Dokkum’s prior record highly credible. “There are many, many other
people who could have ‘discovered’ this where I’d be much more
skeptical,” Ostriker said. “The simplest way of putting it is: His
papers aren’t wrong.”
Not everyone is so convinced. While these UDGs may be large, they’re
not necessarily massive, argue some astronomers. One idea is that UDGs
might be lightweight galaxies that look puffy because they are in the
process of being torn apart by gravitational tides from the rest of the
an astronomer at the University of Surrey, argues that “the only other
place we’ve seen things that are that extreme or more extreme are a
handful of galaxies around the Local Group,” referring to small, dim
“dwarf galaxies” that frequently orbit larger galaxies such as our Milky
Way. “They are all things that are currently being ripped apart.” That
would make most UDGs just large dwarf galaxies in the process of being
ripped to shreds.
Another possibility hinges on the idea that galaxies can “breathe.” At the end of 2015, Kareem El-Badry, who was at the time an undergraduate student at Yale University, proposed that
galaxies can swell out and then collapse in size by over a factor of
two. In this process, gas first falls into the galaxy, forming massive
stars — the breathing in. The stars quickly end their lives in supernova
explosions that blast the gas outside the galaxy — the breathing out.
The gas eventually cools, and gravity pulls it back toward the galactic
center. In a lone galaxy, this rhythm can continue indefinitely. But in
the harsh environment of the Coma cluster, where hot gas fills the space
between galaxies, the gas after the galaxy exhales could be stripped
away, leaving the whole galaxy stuck in a puffy state.
Yet another interpretation, suggested in March 2016 by Harvard University astrophysicists Nicola Amorisco and Avi Loeb, is that UDGs are ordinary galaxies that are just spinning fast. “In our scenario, it’s very natural,” Loeb said.
That idea piggybacks on standard theories of galaxy formation, in
which gas pours into a dark-matter halo to build a galaxy. As the
material falls, it begins to rotate. The amount of rotation determines
the size of the final galaxy. Without much spin, gravity pulls the
galaxy into a compact shape. But galaxies that get a big rotational push
can spin themselves out into large, lightweight disks.
It could be, according to this model, that the UDGs are natural
examples of the very fastest spinners. If so, their stretched-out disks
wouldn’t be dense enough to form as many stars as a slower rotator like
the Milky Way, explaining why they look so faint.
These ideas may well explain some of the UDG population, according to
Abraham. “Probably this is going to evolve into a mixed bag of things,”
he said. But according to his team’s latest data, obtained from
observations that spanned a total of 33.5 hours on the 10-meter Keck II
telescope in Hawaii, there is no evidence that the Dragonfly 44 galaxy
is rotating. In addition, they argue that the total mass of the galaxy
is around a trillion suns — massive enough to prevent it being ripped
apart like a dwarf galaxy, and heavier than the galaxies thought to
periodically puff up.
That mass measurement is the real sticking point, said Philip Hopkins,
a theoretical astrophysicist at the California Institute of Technology
who is preparing several papers on UDGs. It comes from two observations
of different parts of Dragonfly 44. First, the motions of stars in the
galaxy’s inner regions suggest that the area is massive, filled with
dark matter. Second, the outskirts of the galaxy are home to a number of
globular clusters — tight, ancient balls of stars. Just as the number
of stars in a galaxy is ordinarily linked to the amount of dark matter,
observations show that the more globular clusters a galaxy has, the
higher the mass of its dark-matter halo. Dragonfly 44 has Milky
Way-level clusters. Other UDGs seem to have lots of globular clusters,
Because of this, even if these UDGs don’t have heavy dark-matter
haloes, researchers will still be left to explain why they have far more
globular clusters than the known relationship suggests they should. “Something is weird about these things,” Hopkins said. “Either way, it’s really cool.”
The discovery has generated enough interest to earn the team precious
time on the Hubble Space Telescope to study Dragonfly 44’s globular
clusters. “The thing I find hilarious is we’re using humanity’s most
powerful telescope in space to follow up a bunch of telephoto lenses,”
Abraham said. To fully understand the relationship between dark matter
and the globular clusters, though, they have to measure the motions of
the clusters — for which they’ll need to wait until the James Webb Space Telescope launches in 2018.
In parallel, they’re looking to find and characterize more Dragonfly
44s, preferably a few located both outside of a cluster — and thus free
of the harsh cluster environment — and closer to us. It’s an open
question as to whether they exist elsewhere and, if so, what form they
take. “The resolution of whether the UDGs are what we argue they are, or
something else, would come from finding them outside of clusters of
galaxies and seeing how they look there,” Loeb said. A few candidates
have emerged, van Dokkum said, and they are now being followed up with
Keck and Hubble.
For theorists like Ostriker, that’s an exciting prospect. If the
motion of stars in a galaxy like Dragonfly 44 can be studied up close,
it would be a make-or-break test for current dark-matter theories, which
make different predictions about how the missing mass should be
distributed. The leading theory, called cold dark matter, suggests dark
matter should surge at the heart of a galaxy. Right now, though, the
dark-matter-dominated galaxies we have to study are nearby dwarf
galaxies, and they don’t exhibit that characteristic. “Many of the
properties that dark matter is supposed to have … these little galaxies
don’t show,” Ostriker said. “But we say, ‘We don’t really know how these
things were formed anyway,’ and we just change the subject.”
By contrast, an otherwise normal-but-dark Milky Way would eliminate
that loophole. In the universe’s other Milky Way-size galaxies, stars
and gas can outweigh dark matter in the central regions by a factor of
five to one. That makes disentangling the gravitational pull of dark
matter alone tricky. But the center of Dragonfly 44’s disk is 98 percent
dark matter, meaning a map of its central mass would give unprecedented
insight into dark matter’s properties, Ostriker said.
The way forward to understand UDGs isn’t clear yet, Abraham said, but
hopefully at least some of the ideas now being proposed will persist
through the next few years of observations. “In astronomy, it’s still
valid to be just an explorer. In the case of Dragonfly, we’re like Leif
Eriksson,” he said. “You’ve been on the ship for months, and suddenly
somebody said, ‘Land ho!’ And it’s not on the map.”
Image: Astronomers have long known of small dark-matter dominated galaxies.
None were supposed to be as big as ordinary spiral galaxies such as NGC
3810, seen above in negative.
My maths teacher today told us that last summer his car broke down in the highway so he had to pull over. A car stopped by and this guy started to help him, but then while they were talking my teacher said that he taught maths. Suddenly the guy shouts: “MATH PEOPLE DON’T DESERVE ANY HELP” and leaves.
My teacher’s still shocked.
is one of the vital ingredients for life on Earth, scientists want to
know how it got here. One theory is that the water in our solar system
was created in the chemical afterbirth of the Sun. If that were the
case, it would suggest that water might only be common around certain
stars that form in certain ways. But a new study, published today in Science,
suggests that at least some of Earth’s water actually existed before
the Sun was born – and that it came from interstellar space.
That’s certainly something to ponder the next time you drink a glass
of water. But the discovery is also cool because it means water – and
maybe life – may be ubiquitous throughout the galaxy.
“If water in the early Solar System was primarily inherited as ice
from interstellar space, then it is likely that similar ices, along with
the prebiotic organic matter that they contain, are abundant in most or
all protoplanetary disks around forming stars,“ study author Conel
Alexander explained in a press release.
The researchers concluded that a significant portion of Earth’s water
came from interstellar space by looking at the relative abundance of
hydrogen and deuterium.