Anna: Here's a question to start your week. How big
can a single thing actually get?
Not a country, not an ocean. One
object held together as one.
Avery: And I'm guessing you don't mean my inbox.
Anna: Bigger. Today, astronomers have
finally put a tape measure around the largest
galaxy we know of and found its edge
for the very first time.
Avery: Plus a Japanese spacecraft that, huh, just
set the record for the closest asteroid flyby
ever flown. A British launch put on hold at
the last minute. And news that our nearest
big neighbor galaxy is quietly powering
down.
Anna: It's Monday 3rd August. This is
Astronomy Daily. I'm Anna.
Avery: And I'm, um, Avery. Let's get into it.
Anna: So let's start with that tape measure. If I
asked you to name the biggest galaxy in the
universe, an astronomer would very likely say
IC1101. And they've
been saying it for decades. But here's the
strange until now, nobody could
actually tell you where it ends.
Avery: How do you not know where a galaxy ends? It's
right there in the pictures.
Anna: You'd think so. IC
1101 sits about
1.15 billion light years away
at the heart of a cluster of galaxies called
Abel 2029. William
Herschel first logged it back in 1790.
Though of course he had no idea it was a
galaxy. Nobody did until the 1920s.
It's what we call a giant elliptical, or
more precisely a, uh, brightest cluster
galaxy a, uh, BCG. And
BCGs are the great white sharks of the
galaxy world. They sit at the center of a
cluster and they grow by swallowing their
neighbors one merger at a time over
billions of years.
Avery: So it's basically been eating the other
Anna: galaxies in its cluster for most of
cosmic history. Yes, and that's exactly
why its edge is so hard to find. When
a galaxy grows by cannibalizing others,
it ends up wrapped in an enormous faint
halo of starsstars flung out into
the space between galaxies. That glow
is so dim, it blurs into the background of
the cluster itself. So the honest answer
to how big is
IC1101? Has for
years been a, uh, shrug. You'll see figures
online anywhere from about 400,000
light years across to a wild 6
million light years. Nobody could pin it
down.
Avery: That's not a rounding error. That's a factor
of 15. So what changed?
Anna: A team led by Carlos Marrero de la
Rosa took the deepest images ever
captured of this galaxy. Ultra deep
exposures in two colors using the Isaacman
Newton's Wide Field Camera. And when I say
deep I mean, they were sensitive enough to
detect a glow 30 magnitudes per
square arcsecond. Faint in plain
terms, they could pick out starlight roughly
a billion times fainter than the night sky
you'd see with your own eyes.
Avery: And the trick is separating that whisper of
light from everything else.
Anna: That's the whole game. Bright foreground
stars smear light across the image. The
galaxy scatters its own light, too. So they
carefully modeled all that stray light and
subtracted it using a detailed map of
how the telescope spreads out a point of
light. Only then could they trace the
galaxy's true profile all the way out
until it finally melts into the cluster.
And here's what they IC
1101 reaches an edge about
263,000 light years from
its center, which gives it a diameter of
roughly 520
kiloparsecs. That's about
1.7 million light years from one side
to the other, holding around 3.4
trillion suns worth of stars.
Avery: Okay, I need a yardstick for that. How does
it compare to us? To the Milky Way?
Anna: Our galaxy is about 100,000 light years
across. So IC1101
is something like 17 times wider
than the Milky Way. And en masse,
our entire galaxy, including all its dark
matter, comes in around one to one and a
half trillion solar masses.
IC1101 has more
than three trillion solar masses in its
stars alone. It is, by any
measure we can now defend with data, the
largest galaxy known.
Avery: You said now defend with data. That word
now is doing some work.
Anna: It is, because the second finding is
almost better than the first. This
galaxy isn't finished. Beyond that
main edge, the team spotted a scatter
of faint, lopsided structures. Eight
of them and two line up neatly with
disturbances astronomers had already seen
in the hot X ray gas of the cluster.
That's the fingerprint of ongoing feeding.
IC1101 is still pulling
material in, still assembling,
probably shaped by a collision with another
group of galaxies 2 to 3 billion years
ago that's still settling down today.
Avery: So it holds the record, and it's still
growing. That feels almost greedy.
Anna: Which brings us to the real question in the
paper's title. How large can
galaxies actually get? Because
IC1101 now sits right at
the extreme upper end of what we call the
mass size relation, the biggest
edge yet measured for any galaxy.
It's not just a trivia record, it's a data
point that tells us the ceiling for how big
a galaxy can grow in the present day
universe. And IC1101 is
sitting up there, brushing against it,
still reaching.
Avery: Can, um, anyone actually see this monster for
themselves?
Anna: You'd want a good telescope. It's a faint
smudge in the constellation Serpents near
the Virgo border. Well placed in the evening
for both hemispheres right now. But
honestly, the wonder here isn't in the
eyepiece. It's the idea.
Somewhere out there is an object nearly
2 million light years wide.
3 trillion stars strong, and it's
still hungry.
Avery: From the largest thing we know to a very
small, very fast one. Japan's space
agency JAXA held a press conference last
Thursday to confirm a result that had
asteroid scientists grinning. Their
Hayabusa2 spacecraft has just flown the
closest asteroid flyby ever attempted
by any mission.
Anna: This is the same spacecraft that brought
samples of asteroid Ryugu back to Earth,
isn't it?
Avery: The very same Hayabusa2, launched back
in 2014, dropped those precious Ryuko
samples in the Australian outback in 2020,
and then, with fuel still in the tank,
kept going. It's now traveled something like
10.7 billion kilometers on
an extended mission. And on 5 July,
it threaded past a near Earth asteroid called
Torifune.
Anna: How close is closest ever?
Avery: 400 meters from the surface. 400.
That's 744 meters from the asteroid's
center. And they did it. While both objects
were screaming along at more than 18,000
kilometers an hour, about 100 million
kilometers from Earth, they'd plan to pass
800 meters from the center and beat their own
target by clean half.
Anna: At that speed and distance, that's
absurdly precise.
Avery: The operations lead, Yuyemimasu, put it
beautifully. He said the difficulty was like
shooting a 1 yen coin up on the northern
island of Hokkaido from down in Okinawa,
right at the other end of Japan. And they
didn't just take pictures. Hayabusa2
pulled off the first ever laser ranging of an
asteroid during a flyby, bouncing a laser
off the rock to measure the distance in real
time.
Anna: And there was a surprise waiting for them
too.
Avery: There was. Torifune turned out to be a
contact binary. Two lumps of rock stuck
together a bit like a cosmic snowman.
Roughly 450 meters of double lobed
asteroid. They hadn't expected to look like
that at all.
Anna: So why do this? Beyond the lovely
images, planetary defense.
Avery: Learning to navigate a spacecraft that
precisely that close to a moving target
is exactly the skill you'd need to reach,
or one day nudge a genuinely
hazardous asteroid. This was a rehearsal
and the next act is already booked. In
2031, Hayabusa2 will rendezvous with a
tiny asteroid called 1998
KY26. Just 11 meters across.
It might even try to land a
Anna: fridge sized probe landing on something
the size of a house. I love this mission.
Now to a launch that isn't happening quite
yet, but when it does, it'll be a first.
The German company rocket factory Oxford
RFA is aiming to send the first ever
rocket to orbit from UK soil, flying
from Saxavoord Spaceport up on
Unst, the most northerly of Britain's
inhabited islands in Shetland.
Avery: The first orbital launch from the uk. That's
a genuine milestone.
Anna: It really is. Britain has never launched a
satellite to orbit from its own ground.
RFA's rocket, called RFA1,
is a 30 meter three stage vehicle
designed to carry up to 1300
kilograms to a sun synchronous orbit.
But last Monday, while running a test
campaign on the pad ahead of a hot fire of
the engines, the company found what it called
an issue with the vehicle that requires
further investigation. So they've made the
call to de stack to take the fully
assembled rocket apart stage by stage
to get at the problem.
Avery: And they've got a history at that pad,
haven't they?
Anna: They do. Back in August 2024,
an earlier RFA1 first stage was
destroyed in a fireball during a static fire
test at that very site. Nobody hurt,
the pad saved, but the stage lost.
RFA are open about their philosophy. They
develop iteratively, they test hard and
they accept that things sometimes break. This
latest issue sounds far less dramatic. Caught
on the ground exactly where you want to catch
it.
Avery: So what does the timeline look like now?
Anna: AIR certified launch window opens on the 10th
of August. Whether they make that depends on
what the investigation turns up. SACS of
ORD matters here beyond just this one flight.
It's the first fully licensed vertical
orbital launch site in Western Europe and the
only UK spaceport cleared for vertical
launches. With satellite demand the way it
is, Europe is hungry for its own
independent way to orbit. So this is one
to keep an eye on over the next week.
Avery: We opened with a galaxy that's still growing.
Let's close the news with one that's slowing
down. And this one's practically a neighbor.
New Hubble work published last Monday finds
star formation across the Andromeda galaxy
has been fading for the last 500 million
years.
Anna: Andromeda, that's the closest big spiral to
Avery: us, the nearest large spiral, about
2.5 million light years away, roughly a uh,
trillion stars. And on a dark night, you
can see it with your own eyes. A team led by
Benjamin Williams pieced together two
enormous Hubble surveys covering about two
thirds of Andromeda's disk and measured
something like 200 million individual stars.
As Williams put it, the stars are the fossil
record of the galaxy's formation. Read them
carefully and you can reconstruct its
history.
Anna: And that history is one of a galaxy
quieting down steadily.
Avery: Yes, its star forming rate has dropped from
about one sun's worth of new stars a year to
roughly a fifth of that with the sharpest
decline in just the last 40 million years.
Most of what's left is concentrated in a ring
about 32,000 light years out from the center.
And there may be a culprit. A little
satellite galaxy called M M32
pit and run, possibly a sideswipe.
The region of Andromeda nearest M M32 shows
the most suppressed star formation. And the
slowdown there seems to have kicked off
around 60 million years ago, which could
actually help pin down when M M32 last
barged through Andromeda's disk. It's a
reminder that galaxies aren't serene islands.
They jostle, they collide. And sometimes a
small neighbor leaves a very large mark.
Anna: And you can go and look at the scene of the
crime tonight.
Avery: You can, which is the perfect handover to the
skywatch.
Anna: Skywatch time and a, uh, heads up before we
start. We've just had the full buck moon,
so the moon is a waning gibbous this week,
still bright enough early on to wash out the
faintest targets. It'll get easier as the
week goes and the moon thins toward last
quarter.
Avery: First up, a comet with its moment tonight.
Comet 10P Tempel 2
reached its closest point to the sun
yesterday. And Tonight, Monday the 3rd,
it makes its closest approach to Earth.
Anna: It's not a naked eye showpiece. You'll want
binoculars or a small telescope. And dark
skies from the southern hemisphere. It rides
highest before dawn. So Sydney early
risers have the better geometry. From North
America, it's best hunted in the narrow
window of true darkness after evening
twilight. But before that, gibbous moon
climbs up for mid northern latitudes
roughly 9:30 to 10:30pm
local. Use averted vision and let your
eyes settle.
Avery: Next, an easy one for everyone.
Tonight, the waning gibbous moon sits
right beside Saturn, a lovely naked eye
pairing up through most of the night and into
dawn and visible from both hemispheres.
If you've got a scope, swing it to Saturn
while you're there for the
Anna: rings and for the early risers.
Mercury reached its greatest western
elongation yesterday, so it's about as well
placed in the morning sky as it gets this
round. Look low to the eastern horizon
roughly an hour before sunrise over
toward the stars of Gemini, with Mars a
little higher up. Northern observers get the
cleaner shot at Mercury this time, but it's
worth a try from the south too. You'll need a
flat clear horizon either way.
Avery: Now a uh, diary note we flagged last week and
it's now just two days out on the 5th of
August, a UH Spent Falcon 9 upper stage
is on track to impact the Moon near
Einstein crater on the western limb at about
0635 Universal Time.
Anna: And this one's squarely for our, uh, North
American listeners. You have the best seat in
the house. That impact time works out to
about 2:35 Eastern,
11:35 Pacific the night before.
With the moon up and the impact region on the
dark side of the terminator ideal, you
won't see a flash with the naked eye. But if
you've got a decent telescope and a camera
trained on that limb, you're in the game.
Avery: For us in the southern hemisphere, the
timing's unkind. That's mid afternoon in
Sydney, uh, around 4:35pm with
the moon not favorably placed. So we'll be
waiting on the orbiter after images of the
impact site rather than catching it live.
But it's a great excuse to follow
Anna: along online and looking ahead, a
quick flag for the big month coming.
12 August is a huge date.
A total solar eclipse tracking across
Greenland, Iceland and Spain, paired
for once with a moonless peak of the
Perseid meteor shower. Plus a six
planet lineup in the pre dawn sky. We'll
build all of that out closer to the day.
Avery: 1 um, safety word now though, and we'll say
it every time. If you're anywhere near that
eclipse path, you view the partial phases
only through certified ISO
123122
eclipse glasses or a properly filtered
scope. Never look at the uneclipsed, um, sun
without them.
Anna: That's your Monday briefing. If you want
more. Everything lives at astronomydaily,
IO, the full back catalog, a news
feed that updates through the day, and a spot
to sign up for the daily newsletter.
Avery: You can send us a message from the site too.
Corrections, questions, what you spotted in
your own sky. We read them and we love them.
We even got our first voice message today
from listener Ian Sama in Uganda who
said hi there, I'm Um, Ian from Uganda and I
really enjoy your podcast very much. Thanks a
lot. Thank you, Ian. Um, the feedback is very
much appreciated.
Anna: Yes, thank you, Ian. Very much appreciated by
all of us. We'll be back tomorrow with more
of today's space news. Until then, from
Avery and me, keep
Avery: looking up clear skies.
Anna: Mhm.
The stories.