Cosmology Views

Fastest Star Explained

A recent post (June 10) described the fastest star recorded in the Milky Way.

There is an explanation for this star's velocity but it requires a ridiculous mistake by the astronomer analyzing the star's spectrum.

Some might remember my May 29 post titled Velocity of temperature change.

I suspect that mistake was repeated with this star.

From that fast star story: "hot subdwarf made mostly of helium" was moving at 1200 km/s.

This star apparently had nothing around it, no supernova and no white dwarf. The story proposed they caused this star's velocity and then disappeared.

The astronomer looked at the spectrum and concluded it was a hot subdwarf and it apparently had strong helium lines in the spectrum. No spectrum is provided to justify his conclusions.
Though having no spectrum there is a scenario to match the scenario.

Each star has a thermal radiation spectrum. In simple terms, the frequency at the top of the "hump" before it slopes down to infrared indicates the object's temperature.

This spectrum can have absorption lines from ions on or closely above the photosphere.

There are 2 ways to look at the spectrum.

1) it shows the star's temperature.

2) the expected peak has shifted to the red indicating a red shift and so a velocity.

The story says it is a hot star so the peak frequency would be toward the blue side of frequencies.

I expect this spectrum has the peak further to the right which reflects a lower temperature.

The simple explanation for the story:

This star is much cooler than expected. The change in temperature was assigned a velocity!

If the spectrum were published with a story like this, the mistake would be found. It was not published so we are left with a silly story.

Maybe the spectrum really did shift and the star is really moving at a fast velocity. Only the spectrum reveals the correct answer.

Given this star is apparently isolated, the cool star scenario is more likely.