How this transistor works in this circiut?

While learning about transistors, I've found this circuit. After trying to understand how it works, I've no idea.
Basically, the circuit works using the collapsing magnetic field of a bifilar toroid.
As I understand, transistor works permitting to flow the electricity from collector to emitter, while applying a positive voltage to the base.
Basically I'm used to see an oscillator (like a 555), sending the on/off signal to the base of the collector.

In this circuit I cannot understand how the on/off signal is created. Maybe combining the resistor and capacitor to create a RC charge/discharge?
All information is welcome, because I don't understand anything.

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This circuit is called Joule thief

hi Sparky,
As bananasiong states its known as a joule thief in the circuit, Google Joule Thief

Its common name is a Blocking Oscillator.

https://www.prc68.com/I/JouleThief.shtml

Thanks for all the answers.
Maybe is similar like this circuit?
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The main question is how the base of the transistor is switched on and off.

As far I know, I think the pulses are being sent into the base of the transistor by the RC combination. Without the 555 IC, anyone can send pulses with this simple circuit?