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3 votes

How to test for possible negative mass of dark matter?

The paper you mention, Farnes 2018, provides an unconventional idea to explain both dark matter and dark energy. However, this idea has quickly been refuted, e.g. by Stepanian 2019 or by Socas-Navarro ...
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1 vote

Can Jupiter turn into a star if it radiated off enough heat?

Stellar ignition is a very complex matter since it relies on quantum tunneling. It is not an on/off state - ie you add one gram and then, boom, it explodes into a star. The higher density you get, the ...
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5 votes

Why are there three bright spots in the first picture of Sagittarius A*?

Imaging artifacts This image is created by complex image reconstruction algorithms that propose alternative solutions which are averaged. Some of these alternatives do not show a ring structure but ...
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3 votes
Accepted

What implications to cosmology would it have if Webb Telescope probing the far end of our observable Universe finds out a large number of galaxies?

The current "bottom-up" idea of structure formation suggests that galaxies are built up over cosmic time from the mergers of lots of smaller galaxies. There is now plenty of chemical and ...
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1 vote
Accepted

Does the Milky Way have any impact on Earth?

If our sun was a bowling ball in the hands of the player, the earth would be a grape's seed at one of the pins. The next nearest star (another bowling ball) would be 6000 km away. So, except for the ...
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0 votes

About the non-intuitive announcement at 12 May 2022 of the EHT team that spin axis of Sgr A* Black Hole facing Earth?

This recent Nature publication seems to contradict the EHT claim in their presentation about the orientation of the Sgr*A BH accretion disc plane relative to the Galactic plane. Seems to me that gas ...
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6 votes

Can Jupiter turn into a star if it radiated off enough heat?

No. It lacks sufficient mass. Stellar ignition requires a mass of 6-8% of 1 solar mass. Or 70-80 times Jupiter's mass
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32 votes
Accepted

Can Jupiter turn into a star if it radiated off enough heat?

The smallest objects (given an elemental abundance mixture appropriate to a giant planet like Jupiter) that can attain hot enough interiors to ignite a sustained thermonuclear reaction are about 13 ...
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8 votes

About the non-intuitive announcement at 12 May 2022 of the EHT team that spin axis of Sgr A* Black Hole facing Earth?

I think what you mean is that the spin axis of the black hole is not aligned with spin axis of the Milky Way? NB: That's about all you can say - the conclusion of the actual science paper (Akiyama et ...
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0 votes

What does $C^{XY}_{\ell}$ mean when we weasure $a_{\ell m}$ in the sky?

It seems to be a mix between the 2 observales but are the π‘Žπ‘‹β„“π‘š and (π‘Žπ‘Œβ„“π‘š)βˆ— are measured like in the first case in eq(1) with eq(2) ? Yes, for example say $X$ was temperature, then $a_{\ell m}^X$...
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34 votes

Why are there three bright spots in the first picture of Sagittarius A*?

According to the imaging data release paper (Akiyama et al. 2022, ApJL, 930, L14), about the only thing that can be reliably taken from this image (which is a kind of time-averaged composite based on $...
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22 votes

Why are there three bright spots in the first picture of Sagittarius A*?

I don't think anybody knows. Take details of these images with a great deal of skepticism. Just reconstructing any image from the EHT is extremely difficult. There probably are hot spots running ...
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0 votes

Can someone explain exactly what Bates is doing on page 42 of Fundamentals of Astrodynamics?

It turns out I made a few mistakes that threw my answer. I used $5.98\times 10^{25}kg$ instead of $5.98\times 10^{24}kg$ when calculating $\mu$ and TU. That really threw the numbers. I assumed he ...
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2 votes

Which type of star is most effective for solar power?

If you are using photovoltaic cells then all you care about is the flux of energy above the band gap in your photovoltaic devices. Even for sunlight, about 50% falls below this (wavelengths above ...
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0 votes

Which type of star is most effective for solar power?

In general, the more luminosity - the more energy - the more power. So, according to standard stellar classification, stars in class O have a effective temperature β‰₯ 30,000 K and a luminosity β‰₯ 30,...
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1 vote

Which type of star is most effective for solar power?

Only the luminosity of star and the distance to it go into your problem (the power collected would be proportional to the luminosity and inversely proportional to the square of the distance). If you ...
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1 vote

Help in understanding how general relativity describes space-time near black hole poles that emit astrophysical jets

Relativistic jets observed in quasars (and other black holes) are not fully understood, but there is consensus around the basics. Matter falls towards a rotating black hole from an accretion disk. ...
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2 votes

How do BAOs provide evidence for dark matter?

I don't think there is a direct connection to dark matter. Take this figure from the first observation paper: The top three fits (green, red, blue) are models with baryonic matter and dark matter, ...
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0 votes

What is the largest hollow structure that could be made before gravity becomes a problem?

Any size works. The mass of your spherical shell grows like its area, i.e. like radius $r^2$. But gravity drops like $1/r^2$, and the gravitational field of any spherically symmetric mass distribution ...
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0 votes

In which direction do the perihelions of the planets show? Is this somehow correlated with the solar apex?

The longitude of perihelion of the planets does not appear to be anything but random. That is unsurprising since the perihelion advances with time at significant but different rates for the planets, ...
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1 vote

Why are galaxies much closer spaced (relative to their size) than stars?

I think the answer is not in the spacing, it is in their relative sizes and their constituents. Galaxies and (proto)stars begin their lives with very similar separations compared with their sizes, but ...
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1 vote

Does the HD1 Quasar explain how Super Massive Black Holes Form?

The paper by Pacucci et al. (2022) is much more cautious in unequivocally attributing a quasar/supermassive black hole status to HD1; they suggest an intense starburst may be responsible for some or ...
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0 votes

Does the HD1 Quasar explain how Super Massive Black Holes Form?

The galaxy HD1 has a 150M SM BH at its core There have been other explanations suggested for the property leading to that idea and I don't think there's widespread agreement on the black-hole idea at ...
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1 vote

Have solar wind particles escaped the Sun's gravity or will they eventually return back?

The experimental answer is simple: we see the solar wind flowing away, and we see no return flow. It is thus apparent that it is escaping. It's a magnetized plasma: electromagnetic forces, not gravity,...
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0 votes

Have solar wind particles escaped the Sun's gravity or will they eventually return back?

Particles in the solar wind are frequently charged, and in the vacuum of space might remain charged for a LONG time. Such particles are affected by gravity, electric field, and take a curved ...
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0 votes

Does magnetism play a role in the formation of galaxies?

Magnetic fields posses an energy density of $\frac{1}{2\mu_0}|\vec{B}|^2$ This Energy has a generates a gravitational pull. Contributing to the formation of galaxies.
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1 vote

Apparent diameter of Sun

You have your answer in the question. The apparent radius of the Sun, as viewed from far away, is increased by a factor of $(1 - r_s/r)^{-1/2} \simeq 1.0000021$. Yes, the answer is modified very ...
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0 votes

Have solar wind particles escaped the Sun's gravity or will they eventually return back?

Gravitational laws hold, and the solution for the trajectories of massive bodies are conic sections: Look at the answers in this question. There are stable orbits and trajectories that go off to ...
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13 votes

How can a pulsar slow down?

Radiation can indeed take away angular momentum. Thinking about this just from a classical point of view the flux of energy carried by electromagnetic waves (in vacuum) is $$ \vec{S} = \frac{1}{\mu_0} ...
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3 votes

How can a pulsar slow down?

If the pulsar slows down, its angular momentum decreases. This implies that there's some angular momentum radiated away. Rotational energy decreases too, of course. There could be several ...
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