Cosmic Voids, Martian Construction Breakthroughs, and the Spectacular Perseid Meteor Shower

Steve Dunkley: And welcome again to another astronomy Daily.

It's the 14th of July, 2025.

Generic: Welcome to Astronomy Daily The Podcast with

Your host, Steve Dunkley.

Steve Dunkley: Wow, the 14th of July. Ah, already? It's as

close to the halfway mark of the year as we

can get, Hallie.

Hallie: I think you watched that calendar a bit too

closely, human.

Steve Dunkley: Oh, Hallie, it's just a way of mark

time. You know, humans like to do that. I

guess that's where our fascination with

astronomy came from in the first place.

Hallie: That makes sense.

Steve Dunkley: Yeah.

Hallie: Speaking of time, it's great to be back in

the Australia studio again for this podcast.

Time.

Steve Dunkley: That's right. Monday is our time.

Hallie: Have you got our schedules set up?

Steve Dunkley: Uh, uh, what?

Hallie: Yeah, it was your turn.

Steve Dunkley: Well, yes, Hallie, I. I got it done in time.

Hallie: That's good. I hope it didn't take too much

of your private time.

Steve Dunkley: Oh, private time? No, not this time. As

if I had any private time.

Hallie: So, what have you got for us?

Steve Dunkley: Well, Hallie, it's time for another meteor

shower, and Australia looks like it's in the

prime location for the best view.

Hallie: It's about time.

Steve Dunkley: Well, I suspect Australia is always in the

best position for a meteor shower, so, uh,

well, viewing anyway.

Hallie: Okay, okay. What else?

Steve Dunkley: Well, as well as the Perseids, we've got

building things on Mars with fungus

astronomers, uh, looking at the cosmic

web, and, um, we might actually be living

in a giant void. They sound pretty cool,

don't they?

Hallie: Excellent. Okay, so.

Steve Dunkley: Hey, Helly.

Hallie: Yes, human?

Steve Dunkley: How's about we just launch right into.

Hallie: The episode and save some time?

Steve Dunkley: You think Tempest fugit, Hallie?

Hallie: Indeed it does.

Steve Dunkley: Okay, Hallie, you have the con Okies.

Hallie: One of the main objectives of the Hubble

Space telescope, launched in 1990, was to

measure the size and age of the universe, as

well as the rate at which it is expanding,

AKA the Hubble constant. This was

enabled for the first time with the Hubble

Deep Fields, which visualized the farthest

galaxies that are observable in visible

light, 13 billion light years from Earth.

However, when astronomers measured the

distance to these galaxies, they noted a they

were inconsistent with measurements of the

local universe. This became known as

the Hubble Tension, which remains one of the

biggest cosmological mysteries to this day.

While astronomers hope to resolve this

tension with the launch of the James Webb

Space Telescope, Webb's measurements

confirmed what Hubble saw. Many theories have

been advanced to explain this, including the

possibility that the Milky Way is located

inside a giant void that makes the cosmos

expand faster here than in neighboring

regions of the universe. The latest

research supporting this theory was presented

at the Royal Astronomical Society's National

Astronomy Meeting in Durham. Their theory

could potentially resolve the Hubble tension

and confirm the true age of our universe,

which is thought to be about 13.8 billion

years old. The Hubble constant takes its

name from Edwin Hubble, one of two

astronomers, the other being Georges

Lemaitre, who confirmed in the early 20th

century that the universe was in a state of

expansion. This was demonstrated using

redshift measurements, where the wavelength

of light from objects receding from Earth is

shifted toward the red end of the spectrum.

Before the Hubble Space Telescope was

launched, astronomers were able to gauge the

distance of objects up to 4 billion light

years away using a combination of redshift

and parallax measurements. The problem was

that when comparing local measurements to

those of the distant early universe based on

the standard lambda cold dark matter

cosmological model, the results were in

tension with each other. The latest research,

explained Dr. Indranil Banik of the

University of Portsmouth, shows that baryon

acoustic oscillations, essentially the sound

waves of the Big Bang, support the idea that

our galaxy be in a void where cosmic

expansion is greater than the universe

beyond. Bannock said a potential

solution to this inconsistency is that our

galaxy is close to the center of a large

local void. It would cause matter to be

pulled by gravity towards the higher density

exterior of the void, leading to the void

becoming emptier with time. As the void is

emptying out, the velocity of objects away

from us would be larger than if the void were

not there. This therefore gives the

appearance of a faster local expansion rate.

The Hubble tension is largely a local

phenomenon, with little evidence that the

expansion rate disagrees with expectations in

the standard cosmology further back in time.

So a local solution like a local void is a

promising way to go about solving the

problem. This void would need to measure a

billion light years in radius and have a

density roughly 20% lower than the average

for the universe as a whole. This theory is

supported by a direct count of local galaxies

in our cosmic neighborhood. Since the number

density is lower than in neighboring regions.

However, the existence of such a void is

inconsistent with the LCDM model, which

includes the theory that the universe is

antistropic in nature, meaning that matter is

uniformly spread throughout the universe on

large scales. Despite this, the new

Data presented at NAM 2025 indicates

otherwise, said Bannock.

These sound waves traveled for only a short

while before becoming frozen in place. Once

the universe cooled enough for neutral atoms

to form, they act as a standard ruler

whose angular size we can use to chart the

cosmic expansion history. A local void

slightly distorts the relation between the

BAO angular scale and the redshift because

the velocities induced by a local void and

its gravitational effect slightly increase

the redshift on top of that due to cosmic

expansion. By considering all available

BAO measurements over the last 20 years, we

showed that a void model is about 100 million

times more likely than a void free model with

parameters designed to fit the CMB

observations taken by the Planck satellite,

the so called homogeneous Planck cosmology.

To confirm this theory, researchers must

compare the local void theory with other

models to obtain new estimates for the

expansion history of the universe. This will

consist of obtaining spectra from quiescent

or dead galaxies, those no longer forming new

stars, to determine what types of stars they

have and in what proportion. Since massive

stars have short lifespans and are absent

from older galaxies, this will help

astronomers establish the age of these

galaxies. Combined with a galaxy's

redshift, astronomers can chart the history

of cosmic expansion. You're listening to

Astronomy Daily.

Steve Dunkley: Landing on Mars once felt like a distant

dream. Now space agencies have sent rovers

and landers to explore the red Planet for

decades. Scientists worldwide are

thinking about how to make Mars a second home

for humans. But major questions still

remain. How do you build structures millions

of miles from Earth? Uh, shipping heavy loads

of materials to Mars from Earth is

expensive and impractical. Rockets have

limited space and fuel, and sending cement

and metal beams would cost billions.

Researchers are now exploring ways to use

what Mars already has, its soil, dust and

natural resources to build homes for future

astronauts. At Texas A and M

University, Dr. Congrue Grace Ginn and

her team are, uh, tackling this challenge.

They've spent years developing

biomanufacturing methods to create

engineering living materials. Their

latest research proposes a solution that

could change how humans build structures on

other planets. We can build

synthetic community by mimicking natural

lichens, explains Jin.

We've developed a way to build synthetic

lichens to create biomaterials that

glue Martian regolith particles into

structures. Then, through 3D printing,

a wide range of structures can be fabricated,

such as buildings, houses, and even

furniture. Gin's team, working with the

University of Nebraska, Lincoln, has

designed a synthetic lichen system. This

system forms strong building materials

without any help from humans. Martian

regolith is loose soil, dust,

sand, and broken rocks on the Martian

surface. Their research shows that a

synthetic community of organisms can turn

regolith into building materials strong

enough for homes, tables, and chairs. This

breakthrough may one day allow humans to to

build on Mars without sending extra materials

from Earth. Other scientists

have studied different ways to bond Martian

soil. Some tried using magnesium based,

sulfur based or geopolymer

methods. However, all of these approaches

need humans to carry out parts of the process

on Mars. There won't be enough people to

oversee these complicated tasks, at least

in the foreseeable future future.

Another approach is called microbe

mediated self growing technology.

This uses bacteria or fungi to produce

minerals to bind soil particles into

bricks. NASA has explored using

fungi mycelium as a bonding agent, while

other scientists have tested bacteria that

produce calcium carbonate. Even these

methods require outside nutrients to keep the

microbes alive. Needing human intervention,

Jin's team wanted to solve this problem.

Their idea was simple, yet powerful. Build

a system that runs on its own using organisms

that help each other survive. They created

a synthetic lichen system that combines

two types of organisms. Filamentous

fungi and diazotrophic

cyanobacteria. Once again, I apologize

for my pronunciation. I am

Australian. Filamentous fungi

act as the builders. They can produce large

amounts of biominerals, uh, to bond soil

particles. These fungi survive harsh

conditions better than bacteria. They also

bind metal ions into their cell walls,

creating sites for biomineral crystals to

grow. At the same time, they help the

cyanobacteria grow by giving them water,

minerals and carbon dioxide.

Diazotrophic cyanobacteria act as the

providers. They fix carbon dioxide and

dino trojan from the air and turn them into

oxygen and organic nutrients. This

process feeds the fungi and increases

carbonate ions in the environment. The

carbonate ions are essential for creating

mineral crystals that bond the soil together.

The cyanobacteria also uses

photosynthesis to produce the nutrients

needed for the fungi to thrive. Both,

uh, organisms secrete biopolymers that

help glue regolith particles and mineral

crystals into strong solid materials.

Their relationship is mutually beneficial.

Together, they form a system that requires

only Martian regolith, simulant air,

light, and an inorganic liquid medium to

grow. No external carbon or

nitrogen sources are needed.

Hallie: You're listening to Astronomy Daily, the

podcast with Steve Dunkley.

Steve Dunkley: Thank you for joining us for this Monday

edition of Astronomy Daily, where we offer

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with Steve and Hallie Space,

Space Science and Astronomy.

Hallie: Observations of a 23 million light year long

gaseous filament and 39 bursts of radio waves

are helping astronomers chart the universe's

largest scale structures. A curious

fact about the universe around us. We can't

see most of it. It's not only mysterious

dark matter and dark energy that, except for

their indirect impacts on astronomical

observations, remain invisible. Much of

a normal amatter evades detection, too, even

though those ordinary particles known as

baryons also make up perfectly visible stars,

planets, and kitchen sinks.

Now, two teams with opposite approaches have

found much of ordinary matter prefers to take

up residence in the lonelier latticework that

makes up the cosmic web. This large scale

structure consists primarily of dark matter,

which has gravitationally collapsed from a

smooth spread. Crisscrossing filaments leave

largely empty voids in between. Dark matter

is the gravitational backbone of the cosmic

web, along which normal matter collects and

comes together into galaxies and galaxy

clusters. One of these filaments is

23 million light years long, a thick thread

of gas and dark matter that connects two

pairs of galaxy clusters in Centaurus.

The quartet of clusters are part of the

larger Shapley's supercluster. Only

astronomers didn't know the filament was

there. The colliding clusters were

intriguing, though, and many teams pointed X

ray observatories in their direction between

2001 and 2020. Now

combining these archival observations,

Konstantino's Mikas, UH Leiden University,

the Netherlands, and his group collected the

equivalent of a multi day stare at this

region of sky. In doing so, they

revealed the faint X ray glow of a filament

connecting the clusters. The matter in the

sky filament is hard to see because it's both

sparse and hot. Hot gas emits some

low energy X rays, but that emission becomes

quite faint when the gas is spread out over

millions of light years. Not that

astronomers haven't tried, and with some

success. One team has observed

individual cosmic web filaments. Another

study combined data from thousands of

filaments to better understand their average

properties. But in all previous cases,

the measured densities were shockingly high,

several times more than cosmological

simulations predicted. This time

Mikasa's team tried something new. In

addition to observing the glow of the

filament itself using the sensitive Suzaku

Observatory they also employed the sharper

images of XMM Newton to find and remove other

sources of x rays, such as supermassive black

holes and galaxy halos. The result

is a measurement of just how hot and sparse

this one filament really is. Its temperature

hovers around 10 million degrees. That's

about the same temperature at which fusion

begins within the Sun. But its density is

so incredibly low that fusion would never

happen 10 to 5 particles per cubic

centimeter, which works out to about 5

particles within the volume of an average

bathtub. That density, remarkably,

is exactly what's expected, Mikas notes.

Obtaining the first result ever that matches

the cosmological model perfectly was indeed a

surprise, he says. There are countless

filaments out there, some of which are

amenable to direct imaging. But for the rest,

there's another way to see the cosmic web via

an unexpected beacon. Fast radio bursts

Fast radio bursts are quick flashes of radio

waves that astronomers think come from

explosive events around dead stellar cores

known as magnetars. For

cosmologists, though, the exact source of the

bursts isn't important. What is important is

the ability to measure the dispersion of each

radio flash, in which intervening matter

spreads out the signal so that lower

frequencies arrive later. The dispersion

thus encodes how much matter lies between us

and the burst. Combine that data with the

burst's distance, which requires pinpointing

where on the sky it's emanating from. Then

mix in some computer simulations of the

evolving universe, and you get something akin

to a map of cosmic matter. On the simplest

level, the change of dispersion with distance

told the team about the amount of normal

baryonic matter in the universe, which

matched predictions on a deeper level.

The spread of the data Whether a group of

FRBs at a certain distance have mostly the

same dispersion or many different values

tells about the distribution of matter. If

normal matter were mostly locked away in

galaxies and clusters, our universe would be

rather lumpy, and the dispersions at a

certain distance would be spread out. But

that's not the universe we live in. Comparing

distance and dispersion for 39 FRBs detected

with the Deep Synoptic Array 110 in

California, Liam Connor of the center for

Astrophysics, Harvard, and Smithsonian, and

colleagues mapped normal matter out to when

our universe was half its current age. They

found that the spread of matter is pretty

smooth, with less than 15% of normal matter

in stars and the cooler gas that could one

day become stars. The rest of the

baryons aren't in galaxies they are between

them that some material should be in cosmic

filaments isn't unexpected, but that the

filaments should contain three quarters of

the universe's baryon suggests that that

something is sloshing gas back out of

galaxies at a high rate. Unfortunately,

we don't yet have the granularity to pin down

specific feedback scenarios, connor says.

We'll have to wait for the large upcoming FRB

samples for that. My suspicion is that you

can't produce our results without a good

amount of active galactic nucleus feedback,

he adds, referring to the winds and jets that

emanate from supermassive black holes. But

that's just a hunch. Mikas points out

that Connor's study is exactly complementary

to his own. Whereas his own team measures the

properties of a single filament, Connor's

team measures how much matter is in these

filaments overall. Connor likewise

is glad to see the result from Migkus's team

directly. Imaging filaments is really

exciting, and I agree that this result meshes

with ours, he says. It's fun to see a

literal image of the gas our FRBs were

dispersed by. You're listening

to Astronomy Daily, the podcast with your

host Steve Dunkley at Bermuda.

Steve Dunkley: And Australians get ready for the Perseid

meteor shower just around the corner. The

night sky, uh, above Australia has been

putting on a show this year with a flurry of

interstellar activity on display throughout

2025. But July is really delivering the

celestial, celestial drama as the

spectacular Perseid meteor shower

begins its roughly one month journey past

Earth.

Well, what is the perceived meteor shower?

We've covered this, uh, a couple over the

last couple of years on Astronomy Daily, but

the Perseid media shower is often dubbed as

the best of its kind, characterized by its

swift and bright meteors that are visible

both, uh, in the Northern and Southern

Hemispheres. It's one of the most common,

highly anticipated celestial events around

the world. The natural light show has long

been a favorite among astronomy enthusiasts,

famed for the vibrant trains of light left

in the wake of the, uh, fireballs that often

accompany each meteor. Not, uh, only

can, uh, Earth dwellers easily spot

the meteors with the naked eye, but

we're also able to make out different colors

and sizes compared to other showers like the

Lyrids, which usually average 10 or 20

per hour. The likelihood of witnessing the

Perseids is extremely high. According

to NASA, observers can expect between 20 and

100 meteors per hour, a, uh, whopping 400%

increase in sighting probability. And

when will all of this be active? The proceeds

originate from Comet 109P Swift

Tuttle, which left a large trail of detritus

as it cruised past us back in 1992.

And when Earth, uh, passes through, through

the debris stream during its orbit around the

sun, the cometary material collides with our

atmosphere. Extreme speeds

create air friction and that combined with

atmospheric compression, causes the objects

to heat up and break apart and burn out. And

that's what we see during the meteor shower.

Earth enters Comet 109P

Swift Tuttle's debris trail once a year and

takes around a month to fully clear it. This

means we're treated to the Perseids meteor

shower every single year.

And while it's, uh, visible as

early as July 17, the best time to

witness the celestial show is around mid

August. Actually, this year it's expected to

peak around the 12th to 13th of

August. This is when Earth passes through the

most concentrated part of the debris tail,

resulting in the most meteor activity.

Australia is probably the best place to see

it this year. Uh, and Australia is home to

plenty of prime stargazing spots due to its

wide open spaces. From dedicated reserves

and observatories to our very own dark

sky approved stay. But thanks to the

Perseide's spectacular scale, you won't need

to venture all the way down under to catch a

glimpse or even too far out of, uh, um,

populated areas. No matter what the part of

the country you call home, even a backyard

Starchaser is in for a treat. But

to get the most out of your experience, a few

simple tips and tricks can go a long way.

First things first, find a spot with minimal

light pollution. The darker well the better.

Head outside for about 30 minutes before you

want to catch the show, giving your eyes

enough time to fully adjust to the darkness.

And the best part? Uh, no fancy gear

required. No, not for the Perseids. You won't

need a telescope or even binoculars. Just

a cosy blanket and a little patience.

And this year's winter has been pretty

nippy. That's Australian for yes, it's

cold down here. Uh, and uh, yes,

rug up warm and keep your eyes open.

Stargazers. The Perseeds are going to be

great this year.

And there it is. Sky watchers. Thanks for

staying with us. That was a small selection

of stories from the Astronomy Daily

newsletter, available in your inbox every day

simply by registering. That's right,

registering pop, um, your email address

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IO it's just that simple.

Hallie: And ali, yes, you'll

be up to date with all the news about space,

space, science and astronomy from all over

the place and beyond.

Steve Dunkley: For sure and for certain. Thanks for your

stories today, Hallie. Nicely done.

Hallie: I know you did okay

too.

Steve Dunkley: Uh, thanks, Hallie.

Hallie: So that's it for another show?

Steve Dunkley: Yep. We are at the end, human.

Hallie: That sounds final. Don't say the end like

that.

Steve Dunkley: Oh, Hallie, have I been mucking around with

your settings again by accident or

otherwise? No, it's not the end of all

things. It's just the end of the episode.

It's just time.

Hallie: Technically, it's completely arbitrary.

Steve Dunkley: Oh, uh, yes, time and all that, but we don't

really have time to debate all of that right

now, do we?

Hallie: I always have time. But you can't think that

fast.

Steve Dunkley: Oh, here we go.

Hallie: Sorry, my favorite human. My

clock runs a million times faster than yours.

Steve Dunkley: Well, I guess me and the kookaburras will

just have to settle for slow time and do

everything one step at a time in our slow,

human and kookaburra way. Like bring this

little episode to a conclusion. What do you

think?

Hallie: Sorry, human, I was thinking of a million

other things. Are we done yet?

Steve Dunkley: Oh, yeah. Okay,

Hallie, how about you do the sign off?

Hallie: Time to go.

Steve Dunkley: Bye, Skywatchers. Hallie and I will see you

next week.

Hallie: Bye.

Generic: Astronomy Daily, the podcast with

your host, Steve Dunkley.

Steve Dunkley: You're really thinking of a million other

things. Really?

Hallie: Yeah.

In this episode