Bursting with starbirth

September 28, 2017
This image, taken with the NASA/ESA Hubble Space Telescope, shows the galaxy NGC 4490. The scattered and warped appearance of the galaxy are the result of a past cosmic collision with another galaxy, NGC 4485 (not visible in this image). Credit: ESA/Hubble & NASA

This oddly-shaped galactic spectacle is bursting with brand new stars. The pink fireworks in this image taken with the NASA/ESA Hubble Space Telescope are regions of intense star formation, triggered by a cosmic-scale collision. The huge galaxy in this image, NGC 4490, has a smaller galaxy in its gravitational grip and is feeling the strain.

Compared to the other fundamental forces in the Universe, gravity is fairly weak. Despite this, gravity has an influence over huge distances and is the driving force behind the motions of the most massive objects in the cosmos. The scattered and warped appearance of the galaxy in this image, NGC 4490, is a prime example of the results of gravity's unrelenting tug.

Over millions of years, the between NGC 4490 and its smaller neighbour, NGC 4485, has dragged the two closer. Eventually, they collided in a swirling crush of stars, gas, and dust. In this image, this most intense period is already over and the two galaxies have moved through each other, untangled themselves, and are speeding apart again. But gravity's pull is relentless; the galaxies are likely to collide again within a few billion years.

Together NGC 4490 and NGC 4485 form the system Arp 269, which is featured in the Atlas of Peculiar Galaxies. They are located 24 million light-years from Earth in the constellation of Canes Venatici (The Hunting Dogs). The extreme tidal forces of their interaction have determined the shapes and properties of the two galaxies. Once a barred spiral galaxy, similar to the Milky Way, NGC 4490's outlying regions have been stretched out, resulting in its nickname of the Cocoon Galaxy. Virtually no trace of its past spiral structure can be seen from our perspective, although its companion galaxy NGC 4485—not pictured here—still clings on to its spiral arms.

This cosmic collision has created rippling patches of higher density gas and dust within both galaxies. The conditions there are ripe for ; the brilliant pink pockets of light seen here are dense clouds of ionised hydrogen, glowing as they are irradiated with ultraviolet light from nearby young, hot stars. This spectacular burst of new activity has led to NGC 4490's classification as a starburst galaxy.

Star formation is also evident in the thin thread that connects the two galaxies: a bridge of created by the ancient crash, stretching over the 24 000 light-years that currently separate the fated pair. But where there is life, there is also death. Several supernovae have also been spotted in NGC 4490 over the past few decades, including SN 1982F and SN 2008ax.

Explore further: Image: Hubble sees starbursts in the wake of a fleeting romance

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1 / 5 (5) Sep 28, 2017
Re: "Compared to the other fundamental forces in the Universe, gravity is fairly weak. Despite this, gravity has an influence over huge distances and is the driving force behind the motions of the most massive objects in the cosmos."

Friendly reminder: If the Earth was an inch from the Sun, the next nearest star would be 4 MILES away.

And what would be the force of gravity between those two stars? It would be equivalent to 1.5 x 10^-14 Earth gee's.

Attempts to construct a cosmology with such small forces over such extraordinary distances will predictably lead to hypothetical unseen entities like black holes and dark matter, and it will predictably invite theorists to divide volumes of matter by zero in order to strengthen gravity sufficient for it to work at interstellar scales.

The academics will play their games with the numbers, but this basic algebra (and common sense) indicates that gravity is not dominating at the interstellar scale.
1 / 5 (4) Sep 28, 2017
Bankrupting Physics: How Today's Top Scientists Are Gambling Away Their Credibility
Alexander Unzicker and Sheilla Jones (p10, 2013)

"Combing through the library, I found a well-known textbook on galactic dynamics where the authors state:

'It is worth remembering that all of the discussion so far has been based on the premise that Newtonian gravity and general relativity are correct on large scales. In fact, there is little or no direct evidence that conventional theories of gravity are correct on scales much larger than a light year or so. Newtonian gravity works extremely well on scales of 10^12 meters, the solar system (...) It is principally the elegance of general relativity and its success in solar system tests that lead us to the bold extrapolation to scales 10^19 - 10^24 meters ... [3]'"

1 / 5 (4) Sep 28, 2017

"... Wow! Fancy that. Two leading experts claim that the law of gravity has been well tested in our solar system only -- a tiny fraction of the universe that corresponds to a single snowflake in all of Greenland. Scientists seem drawn to the 'elegance' of the theory, which is not really a scientific criterion. I often confront physicists and astronomers with this quote. Usually they shrug and reply airily, 'That is indeed true, but why shouldn't the law of gravity be valid? So far, there is nothing better to replace it.'"

the quoted textbook:

[3] J. Binney and S. Tremaine, S. Galactic Dynamics (Princeton, NJ: Princeton University Press, 2008), 635.

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