I write HTML. Please pass it along.
I grew up in small towns and in the North where the rule is share and share alike. I'm a Creative Commons type of guy. Copy and paste ANY OF MY MATERIAL anywhere you want. Hyperlinks to your own Social Media are at the bottom of each post. This work is licensed under my Creative Commons Attribution 4.0 International License.
.
TO WATCH VIDEOS FULL SCREEN >> SOUND ON >> Start the video and click on the YouTube Icon at the bottom. Later When you close that window you will be brought back here.
The second in a series of videos showcasing the Department of Aeronautics' research in Aerodynamics. This video illustrates the Department's Computational Fluid Dynamics (CFD) research. Professor Peter Vincent talks about how we use computers to solve complex fluid flow problems, with applications across the aerospace and automotive industries, as well as marine and green energy.
To find out more about the research featured in this video, take a look at our website:
https://www.imperial.ac.uk/aeronautic...https://www.imperial.ac.uk/aeronautic...
Follow us on social media for regular updates:
Twitter - https://twitter.com/aeroimperial
Produced by Tom Walker Film - www.tomwalkerfilm.com
A growing catalog of huge but dim
galaxies such as Dragonfly 44 is forcing astronomers to invent new
theories of galactic evolution.
Ultra-diffuse
galaxies somehow lost their star-forming gas, leaving them with only
a skeleton of elderly stars.
Kristina Armitage/Quanta Magazine
Introduction
In 2016, astronomers led by Pieter
van Dokkum of Yale University published a
bombshell paper claiming the discovery of a galaxy so dim, yet so
broad and heavy, that it must be almost entirely invisible. They
estimated that the galaxy, dubbed Dragonfly 44, is 99.99% dark
matter.
A heated debate ensued about Dragonfly 44’s properties that
remains unresolved. Meanwhile, more than 1,000 similarly big but
faint galaxies have turned up.
Dragonfly 44 and its ilk are known as ultra-diffuse galaxies
(UDGs). While they can be as large as the largest ordinary galaxies,
UDGs are exceptionally dim — so dim that, in telescope surveys of
the sky, “it’s a task to filter out the noise without
accidentally filtering out these galaxies,” said Paul Bennet, an
astronomer at the Space Telescope Science Institute in Baltimore. The
bright star-forming gas that’s abundant in other galaxies seems to
have vanished in UDGs, leaving only a skeleton of elderly stars.
Their existence has caused a stir in galactic evolutionary theory,
which failed to predict them. “They didn’t turn up in
simulations,” van Dokkum said. “You have to do something special
to make a galaxy that big and faint.”
Wild new theories have emerged to explain how Dragonfly 44 and
other UDGs came about. And these giant smudges of light may be
providing fresh evidence of dark matter’s invisible hand.
Too Much Dark Matter
Abstractions navigates
promising ideas in science and mathematics. Journey with us and join
the conversation.
As gravity brings clumps of gas and stars together, their combined
energies and momentums cause the mashup to inflate and rotate.
Eventually a galaxy emerges.
There’s just one problem. As galaxies rotate, they should come
apart. They don’t appear to have enough mass — and thus gravity —
to stick together. The concept of dark matter was invented to provide
the missing gravity. In this picture, a galaxy sits inside a larger
conglomeration of nonluminous particles. This dark matter “halo”
holds the spinning galaxy together.
One way to estimate a galaxy’s rotation speed, and thus its dark
matter content, is by counting its spherical clusters of stars. “We
don’t know why, from a theory point of view,” Bennet said, but
the number of these “globular clusters” correlates closely with
those harder-to-measure properties. In the 2016 paper, van Dokkum
counted 94 globular clusters inside Dragonfly 44 — a number that
implied an extraordinarily large dark matter halo, despite how little
visible matter the galaxy has.
No one had ever seen anything like it. Van Dokkum and co-authors
suggested that Dragonfly 44 could be a “failed Milky Way”: a
galaxy with a Milky Way-size dark matter halo that underwent a
mysterious event early on that robbed it of its star-forming gas,
leaving it with nothing but aging stars and a giant halo.
Or No Dark Matter
The object attracted the interest of another camp of astronomers
who argue that dark matter doesn’t exist at all. These researchers
explain galaxies’ missing gravity by tweaking Newton’s law of
gravity instead, an approach called modified Newtonian dynamics, or
MOND.
According to MOND, the modified gravitational force for each
galaxy is calculated from the mass-to-light ratio of its stars —
their total mass divided by their luminosity. MOND theorists do not
speculate as to why the force would depend on this ratio, but their
ad hoc formula matches the observed speeds of most galaxies, without
the need to invoke dark matter.
When news broke about Dragonfly 44, MOND advocate Stacy
McGaugh, an astronomer at Case Western Reserve University,
calculated from its mass-to-light ratio that it should rotate more
slowly than van Dokkum’s initial estimate indicated. The MOND
calculation didn’t seem to fit the data.
More than 1,000 ultra-diffuse galaxies have been identified in
recent years, including (from left) Dragonfly 44, NGC 1052-DF2, and a
close-together pair labeled NGC 1052-DF4 and NGC 1052-DF5.
(left) Teymoor Saifollahi and NASA/HST; NASA/ESA/Pieter van
Dokkum; Judy Schmidt
Introduction
But then in 2019, van Dokkum’s group downgraded Dragonfly 44’s
rotation speed using
improved data. MOND was vindicated. “Dragonfly 44 is an example
of how these data evolve to agree with MOND,” said McGaugh.
Still, for the majority of astronomers, who believe in dark
matter, the slower rotation speed just implied that Dragonfly 44’s
halo is smaller than they thought. In 2020, an independent group
further downsized the halo by counting dramatically
fewer globular clusters, but van Dokkum disputes this result.
Though the halo’s size remains uncertain, it may be less massive
than initially supposed, suggesting that Dragonfly 44 isn’t a
failed Milky Way after all.
Big Old Galaxy
A newly discovered oddity has compounded the mystery.
In a
paper published in August, van Dokkum’s group found Dragonfly
44 to be extremely ancient, having formed between 10 billion and 13
billion years ago.
But such an old galaxy should not be as large as Dragonfly 44 is.
Early-universe objects tend to be more compact because they formed
before the universe’s rapid expansion.
Moreover, such an old, threadbare galaxy should have been
completely torn apart by now. That Dragonfly 44 has held together
implies that it has a hefty dark matter halo after all —
potentially restoring the “failed Milky Way” hypothesis. “That’s
a really fun explanation, so that’s why I like it, but I don’t
know if it’s right,” said van Dokkum.
Another explanation, the “high spin” hypothesis, posits that
two small galaxies merged while rotating in the same direction, such
that the resulting galaxy, Dragonfly 44, acquired the angular
momentum of both. This caused it to rotate more quickly, puffing it
out and blowing out its star-making material.
Dazzlingly Diverse UDGs
Amid the scrutiny of Dragonfly 44, astronomers have also cataloged
a vast and diverse collection of other ultra-diffuse galaxies. The
findings are forcing them to conclude that galaxies form in more ways
than they knew.
Some newfound UDGs seem to lack dark matter entirely. Van Dokkum’s
group identified
one such galaxy in 2018, then spotted a trail of others nearby.
This May, the team conjectured
in Nature that the trail formed in a long-ago collision of
two galaxies. The collision slowed down the flow of the galaxies’
gas, but their dark matter kept going as if nothing had happened. The
gas then compressed into clumps of stars, eventually forming a string
of dark matter-free galaxies.
The Dragonfly Telephoto Array, a multi-lens telescope located in
New Mexico, is capable of spotting faint objects in the night sky.
Project Dragonfly
Meanwhile, Bennet discovered
two UDGs in 2018 that point to a different formation theory. In
each case, tidal forces from a heavy nearby galaxy seem to have
ripped through the UDG, puffing it out and stealing its gas. (This
can’t explain Dragonfly 44, which sits too far from heavy
galaxies.)
Puzzlingly, a
September paper reported recent star formation in a UDG,
contradicting the idea that they only harbor old stars.
Such a range of UDGs that look the same outwardly but differ
internally may validate dark matter theory over MOND. “If the stars
are moving very fast in one galaxy, and very slowly in the other,
that’s a big problem for those alternative theories,” van Dokkum
said.
McGaugh agreed that if there are “genuine outliers” among the
UDG population, “that is indeed a problem for MOND.” However, he
added, “that doesn’t automatically make dark matter a better
interpretation.”
Definitive answers will require new telescopes. The newly
operational James Webb Space Telescope has already spotted distant
galaxies as they appeared when they were forming in the early
universe, which will help test and refine the nascent ideas.
“The big takeaway is that we still don’t know what’s out
there,” van Dokkum said. “There are galaxies that we haven’t
discovered that are very big, very close by, and have unusual
properties, and they are not in our current catalogs even after all
these decades of studying the sky.”
Also on Quanta Magazine
Quanta Magazine
10 days ago
3 comments
Svetlana Jitomirskaya was born in
Ukraine, but left the Soviet Union to escape …
A Dream of Discovering Alien …
8 days ago
7 comments
For Lisa Kaltenegger and her
generation of exoplanet astronomers, decades of …
Quanta Magazine
2 days ago
2 comments
Lattice cryptography promises to
protect secrets from the attacks of …
Quanta Magazine moderates comments to facilitate
an informed, substantive, civil conversation. Abusive, profane,
self-promotional, misleading, incoherent or off-topic comments will
be rejected. Moderators are staffed during regular business hours
(New York time) and can only accept comments written in English.
It's
well understood that from the surface of the Earth the curvature
of the planet is not readily visible, but, as you travel higher
the shape of the world becomes apparent to a casual glance. So I
wanted to actually quantify this in an visual form using
Youtube's 360 Video feature, it's obviously best experienced
through a VR headset, or a 'Cardboard' style viewer, but you can
also use the web browser if you just want to appreciate the
visuals. Music 'Future Memory' by Test Shot Starfish
>>>>>>>>>>>>>>
Pocket
worthyStories to fuel your mind
“What
If?” 11 Serious Answers to Slightly Crazy Science Questions
What
if the dinosaurs had survived—or all viruses suddenly disappeared?
What if the planet was made of blueberries, or gravity stopped
working?
What
if there were no stupid questions? (There aren’t.) Turns out you
can learn a lot about science by trying to find earnest answers to
wildly hypothetical, vaguely absurd scenarios. Even the most
outlandish thought experiments can provide insight into how the world
works. So let your imagination run wild with this curated collection
exploring eleven out-there scientific “What Ifs?”
Not
all of history's most significant scientists were college graduates
when they began their works. In fact, history is full of scientists
who have shaped the world due to their work as teenagers. If they
were disregarded simply because of their age, many things we take for
granted today may not exist. Through their own determination and
thirst for knowledge, these teenagers impacted the world far greater
than they would realize long after their deaths.
1.
Isaac Newton
- During Newton's formative years, it was common place for the young
man to develop various devices while attending school. His devotion
to studies and high marks in school were impressive to many. Although
his mother attempted to make a farmer of him by removing young Isaac
from school, the schoolmaster and his uncle suggested to his mother
that he return to school to finish his education. Isaac Newton
attended Cambridge University upon finishing school in 1661. He
developed a variety of scientific methods and discoveries including
those in optics and colors.
2.
Albert Einstein - In his younger years, Albert Einstein had
always shown a great interest in mathematics and science. Einstein
attended the Swiss Federal Polytechnic examinations in Zurich.
Although his scores were below standard in many of the required
subjects, his mathematics and physics skills were exceptionally high.
From there, Albert Einstein attended Aargau Cantonal School in Aarau,
Switzerland where he graduated with passing grades in some subjects
and receiving the highest grade scale possible in mathematics and
physics. His theories have laid the ground work for many scientists
of today and is most notable for the Theory of Relativity.
3.
Galileo Galilei
- While at the University of Pisa studying for a medical degree at
the age of 17, Galileo Galilei became enthralled with how movements
of air currents could cause a chandelier to sway in a rhythmic
pattern. Setting up a set of differentiating pendulums, Galileo
discovered that regardless of the size difference the pendulums kept
time with each other. The young man changed his degree from medical
sciences to mathematics after attending a lecture on geometry. A the
age of 22, Galileo published a book on the design of a hydrostatic
balance he had invented.
Experiments
in evolution are exploring what would happen if we rewound the tape
of life.
ow
was it? Save stories you love and never lose them. B -0 vb
4.
Aristotle -
In the 3rd Century BCE, Aristotle had made great contributions to
nearly every subject of study. At the age of 18, he attended Plato's
Academy where he studied nearly every subject offered at the time.
For 20 years he remained at the Academy until eventually quitting.
With his vast knowledge of subject material, Aristotle had completed
encyclopedias of information opening the doors for many.
5.
Blaise Pascal - Did you know that your Windows-based computer
system has a tool installed that was invented 350 years ago? Blaise
Pascal began work on calculating devices and prototypes at the age of
16, in 1642. Although the centuries have developed calculators that
are digital, solar powered, scientific, and software-based Pascal set
the wheels in motion with the development of earlier versions of our
calculating devices. What computer or smartphone would be complete
without a calculator of some kind?
It
goes to show that discouraging a child from using his or her
imagination and exploring other possible answers to questions could
have repercussions in the future of humanity. The argument can be
made that if one person hadn't invented a particular theory or
device, someone else would have. However, could we believe that it
would be the same product if it came from a completely different
perspective of a different inventor?
Ken
Myers is an expert advisor on in-home care & related family
safety issues to many websites and groups. He is a regular
contributor to www.gonannies.com.
The
views expressed are those of the author(s) and are not necessarily
those of Scientific American.
It's well understood that from the
surface of the Earth the curvature of the planet is not readily
visible, but, as you travel higher the shape of the world becomes
apparent to a casual glance. So I wanted to actually quantify this in
an visual form using Youtube's 360 Video feature, it's obviously best
experienced through a VR headset, or a 'Cardboard' style viewer, but
you can also use the web browser if you just want to appreciate the
visuals. Music 'Future Memory' by Test Shot Starfish
:extract_focal()/https%3A%2F%2Fs3.amazonaws.com%2Fpocket-collectionapi-prod-images%2F6a72093f-ce79-4f8d-b2bc-a315152be67d.jpeg)