Connect with us

Mobile phones are so ubiquitous that we typically don’t think about how they work. They just do, much to our benefit, and sometimes annoyance. But the key to their function is a vast array of radio transmission towers. These cell towers span a large percentage of Earth’s land surface, particularly in heavily populated areas, and they transmit microwave signals all the time. With all those cell towers emitting all those radio signals, a fun question to ask is whether those signals could be detected by an alien civilization.

The answer to this question was recently published in the Monthly Notices of the Royal Astronomical Society, and it’s worth the read. The paper starts by noting how the radio signals streaming into space have changed. In the 20th century, the bulk of radio transmissions were those from commercial radio and television stations. Now those transmissions are dwarfed by those of mobile communications. Military radar transmissions are still the most powerful source of Earth’s radio leakage, but cell towers now fill the second position.

Each cell tower emits a radio signal with a power of 100 – 200 Watts. Given the number of towers and the amount of radio leakage, that amounts to a few gigawatts beamed into space. If we assume an alien civilization has sophisticated radio astronomy, similar to our Event Horizon Telescope, then our transmissions should be detectable within a dozen light-years or so.

But that depends on where the aliens are in our sky. Cell towers emit most of their radio power parallel to the surface of the Earth, so a tower signal is strongest when it is rising or setting as seen from the alien star. And since the majority of towers are in the northern hemisphere, an alien star in the northern hemisphere will get a stronger signal than one in the southern hemisphere.

One other complication is all the tower signals are different, and they overlap in such a way that an alien civilization wouldn’t be able to distinguish any specific messages. You don’t need to worry about aliens listening in on your personal phone calls. But they could still use the signals to find out some interesting things about Earth. Since the distribution of towers roughly corresponds to our population distribution, the aliens could get a measure of Earth’s rotation and axial tilt. They would also have a measure of Earth’s land distribution, and over time could study how our population distributions change.

hd95735 1024x614 2
Calculated Earth signal as seen from HD 95735, about 8 light-years from Earth. Credit: Saide, et al

As an example, the team modeled signals as seen from three nearby stars. Alpha Centauri is in the southern hemisphere, but just 4 light-years away, so it should get a measurable signal from us. Barnard’s Star (6 light-years away) and HD 95735 (8 light-years away) are in the northern hemisphere, and would likewise get good radio data from Earth. All three of these star systems are known to have planets, though none are known to have a potentially habitable world.

As humanity transitions to more modern mobile technology such as 5G, tower signals will become even stronger, which means even more nearby stars would have a detectable signal from Earth. It may be just a matter of time before our phone signals reach out and touch alien minds.

Reference: Saide, Ramiro C., M. A. Garrett, and N. Heeralall-Issur. “Simulation of the Earth’s radio-leakage from mobile towers as seen from selected nearby stellar systems.” Monthly Notices of the Royal Astronomical Society (2023): stad378.

The post Aliens Could Map Earth From its Mobile Phone Towers appeared first on Universe Today.

Did you miss our previous article…
https://mansbrand.com/these-stars-are-already-merging-but-their-future-will-be-catastrophic/

Continue Reading

Frontier Adventure

Gravastars are an Alternative Theory to Black Holes. Here’s What They’d Look Like

gravastar jpg

One of the central predictions of general relativity is that in the end, gravity wins. Stars will fuse hydrogen into new elements to fight gravity and can oppose it for a time. Electrons and neutrons exert pressure to counter gravity, but their stability against that constant pull limits the amount of mass a white dwarf or neutron star can have. All of this can be countered by gathering more mass together. Beyond about 3 solar masses, give or take, gravity will overpower all other forces and collapse the mass into a black hole.

While black holes have a great deal of theoretical and observational evidence to prove their existence, the theory of black holes is not without issue. For one, general relativity predicts that the mass compresses to an infinitely dense singularity where the laws of physics break down. This singularity is shrouded by an event horizon, which serves as a point of no return for anything devoured by the black hole. Both of these are problematic, so there has been a long history of trying to find some alternative. Some mechanism that prevents singularities and event horizons from forming.

One alternative is a gravitational vacuum star or gravitational condensate star, commonly called a gravastar. It was first proposed in 2001, and takes advantage of the fact that most of the energy in the universe is not regular matter or even dark matter, but dark energy. Dark energy drives cosmic expansion, so perhaps it could oppose gravitational collapse in high densities.

gravastar 1 jpg
Illustration of a hypothetical gravastar. Credit: Daniel Jampolski and Luciano Rezzolla, Goethe University Frankfurt

The original gravastar model proposed a kind of Bose-Einstein condensate of dark energy surrounded by a thin shell of regular matter. The internal condensate ensures that the gravastar has no singularity, while the dense shell of matter ensures that the gravastar appears similar to a black hole from the outside. Interesting idea, but there are two central problems. One is that the shell is unstable, particularly if the gravastar is rotating. There are ways to tweak things just so to make it stable, but such ideal conditions aren’t likely to occur in nature. The second problem is that gravitational wave observations of large body mergers confirm the standard black hole model. But a new gravastar model might solve some of those problems.

The new model essentially nests multiple gravastars together, somewhat like those nested Matryoshka dolls. Rather than a single shell enclosing exotic dark energy, the model has a layers of nested shells with dark energy between the layers. The authors refer to this model as a nestar, or nested gravastar. This alternative model makes the gravastar more stable, since the tension of dark energy is better balanced by the weight of the shells. The interior structure of the nestar also means that the gravitational waves of a nestar and black hole are more similar, meaning that technically their existence can’t be ruled out.

That said, even the authors note that there is no likely scenario that could produce nestars. They likely don’t exist, and it’s almost certain that what we observe as black holes are true black holes. But studies such as this one are great for testing the limits of general relativity. They help us understand what is possible within the framework of the theory, which in turn helps us better understand gravitational physics.

Reference: Jampolski, Daniel and Rezzolla, Luciano. “Nested solutions of gravitational condensate stars.” Classical and Quantum Gravity 41 (2024): 065014.

The post Gravastars are an Alternative Theory to Black Holes. Here’s What They’d Look Like appeared first on Universe Today.

Did you miss our previous article…
https://mansbrand.com/japans-new-h3-rocket-successfully-blasts-off/

Continue Reading

Frontier Adventure

Japan’s New H3 Rocket Successfully Blasts Off

240125 slim moon3 1024x513 1 jpg

Japan successfully tested its new flagship H3 rocket after an earlier version failed last year. The rocket lifted off from the Tanegashima Space Center on Saturday, February 17, reaching an orbital altitude of about 670 kilometers (420 miles). It deployed a set of micro-satellites and a dummy satellite designed to simulate a realistic payload.

With the successful launch of the H3, Japan will begin transitioning away from the previous H-2A rocket which has been in service since 2001 and is set to be retired after two more launches. Several upcoming missions depend on the H3, so this successful test was vital.

The launch came after two days of delays because of bad weather. The H3 rocket, built by Mitsubishi Heavy Industries, is now set to become the main launch vehicle of Japan’s space program. The rocket’s first flight in March 2023 failed to reach orbit, which resulted in the loss of an Earth imaging satellite.

The successful launch and deployment of the satellites was a relief for JAXA and members of the project. A livestream of the launch and subsequent successful orbit insertion showed those in the JAXA command cheering and hugging each other.

“I now feel a heavy load taken off my shoulders,” said JAXA H3 project manager Masashi Okada, speaking at a press briefing after the launch. “But now is the real start for H3, and we will work to steadily improve it.”

H3 stands about 57-meter (187-feet) tall and is designed to carry larger payloads. The two microsatellites were deployed approximately 16 minutes and 43 seconds after liftoff. They included an Earth observation satellite named CE-SAT-IE, developed by Canon Electronics, and TIRSAT, an infrared Earth observation instrument that will observe the temperature of the Earth’s surface and seawater.

“We feel so relieved to be able to announce the good results,” JAXA President Hiroshi Yamakawa said at the briefing. Yamakawa added that the main goals of H3 are to secure independent access to space and allow Japan to be competitive as international demand for satellite launches continues to grow. “We made a big first step today toward achieving that goal,” he said.

Image of SLIM lander on moon
An image sent back by a mini-probe shows Japan’s SLIM lander on its side on the lunar surface. (JAXA / Takara Tomy / Sony Group / Doshisha Univ.)

The successful launch comes after two other recent successes for JAXA last month where the H-2A rocket successfully placed a spy satellite into orbit, and just days later JAXA’s robotic SLIM (Smart Lander for Investigating Moon) made the first-ever precise “pinpoint” Moon landing – although unfortunately the lander came down on its side. However, during the final stages of the descent two autonomous rovers were successfully deployed: a tiny hopping robot and the other designed to roll about the surface. Both have sent back pictures and can continue exploring and sending back information even if SLIM cannot be operated.

The post Japan’s New H3 Rocket Successfully Blasts Off appeared first on Universe Today.

Did you miss our previous article…
https://mansbrand.com/european-satellite-ers-2-to-reenter-earths-atmosphere-this-week/

Continue Reading

Frontier Adventure

European Satellite ERS-2 to Reenter Earth’s Atmosphere This Week

ERS 2 reentry how and why is it happening pillars 1024x576 1 jpg

One of the largest reentries in recent years, ESA’s ERS-2 satellite is coming down this week.

After almost three decades in orbit, an early Earth-observation satellite is finally coming down this week. The European Space Agency’s (ESA) European Remote Sensing satellite ERS-2 is set to reenter the Earth’s atmosphere on or around Wednesday, February 21st.

Trail Blazing Mission

Launched atop an Ariane-4 rocket from the Kourou Space Center in French Guiana on April 21st, 1995, ERS-2 was one of ESA’s first Earth observation satellites. ERS-2 monitored land masses, oceans, rivers, vegetation and the polar regions of the Earth using visible light and ultraviolet sensors. The mission was on hand for several natural disasters, including the flood of the Elbe River across Germany in 2006. ERS-2 ceased operations in September 2011.

Reentry
Anatomy of the reentry of ERS-2. ESA

ERS-2 was placed in a retrograde, Sun-synchronous low Earth orbit, inclined 98.5 degrees relative to the equator. This orbit is typical for Earth-observing and clandestine spy satellites, as it allows the mission to image key target sites at the same relative Sun angle, an attribute handy for image interpretation.

Ice
ERS-2 tracks and ice floe. ESA

The Last Days of ERS-2

Reentry predictions for the satellite are centered on February 21st at 00:19 Universal Time (UT)+/- 25 hours. As we get closer, expect that time to get refined. The mass of ERS-2 at launch (including fuel) was 2,516 kilograms. Expect most of the satellite to burn up on reentry.

Orbit
The orbital path of ERS-2. Orbitron

For context, recent high profile reentries include the UARS satellite (6.5 tons, in 2011), and the massive Long March-5B booster that launched the core module for China’s Tiangong Space Station in late 2022 (weighing in at 23 tons).

ERS2
ERS-2 in the clean room on Earth prior to launch. ESA

ESA passed its first space debris mitigation policy in 2008, 13 years after ERS-2 was launched. In 2011, ESA decided to passively reenter the satellite, and began a series of 66 deorbiting maneuvers to bring its orbit down from 785 kilometers to 573 kilometers. Its fuel drained and batteries exhausted, ERS-2 is now succumbing to the increased drag of the Earth’s atmosphere as we near the peak of the current solar cycle.

North Prague Floods ERS

Continue Reading

Trending